docs: remove "Migrating from v1" section from README (#1070)

The migration guidance has outlived its usefulness now that v2 has been
the recommended version for a long time. Drop the section to keep the
README focused on current usage.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: pelletier

README.md

@@ -314,304 +314,6 @@ Multiple versions are available on [ghcr.io][docker].
 
 [docker]: https://github.com/pelletier/go-toml/pkgs/container/go-toml
 
-## Migrating from v1
-
-This section describes the differences between v1 and v2, with some pointers on
-how to get the original behavior when possible.
-
-### Decoding / Unmarshal
-
-#### Automatic field name guessing
-
-When unmarshaling to a struct, if a key in the TOML document does not exactly
-match the name of a struct field or any of the `toml`-tagged field, v1 tries
-multiple variations of the key ([code][v1-keys]).
-
-V2 instead does a case-insensitive matching, like `encoding/json`.
-
-This could impact you if you are relying on casing to differentiate two fields,
-and one of them is a not using the `toml` struct tag. The recommended solution
-is to be specific about tag names for those fields using the `toml` struct tag.
-
-[v1-keys]: https://github.com/pelletier/go-toml/blob/a2e52561804c6cd9392ebf0048ca64fe4af67a43/marshal.go#L775-L781
-
-#### Ignore preexisting value in interface
-
-When decoding into a non-nil `interface{}`, go-toml v1 uses the type of the
-element in the interface to decode the object. For example:
-
-```go
-type inner struct {
-	B interface{}
-}
-type doc struct {
-	A interface{}
-}
-
-d := doc{
-	A: inner{
-		B: "Before",
-	},
-}
-
-data := `
-[A]
-B = "After"
-`
-
-toml.Unmarshal([]byte(data), &d)
-fmt.Printf("toml v1: %#v\n", d)
-
-// toml v1: main.doc{A:main.inner{B:"After"}}
-```
-
-In this case, field `A` is of type `interface{}`, containing a `inner` struct.
-V1 sees that type and uses it when decoding the object.
-
-When decoding an object into an `interface{}`, V2 instead disregards whatever
-value the `interface{}` may contain and replaces it with a
-`map[string]interface{}`. With the same data structure as above, here is what
-the result looks like:
-
-```go
-toml.Unmarshal([]byte(data), &d)
-fmt.Printf("toml v2: %#v\n", d)
-
-// toml v2: main.doc{A:map[string]interface {}{"B":"After"}}
-```
-
-This is to match `encoding/json`'s behavior. There is no way to make the v2
-decoder behave like v1.
-
-#### Values out of array bounds ignored
-
-When decoding into an array, v1 returns an error when the number of elements
-contained in the doc is superior to the capacity of the array. For example:
-
-```go
-type doc struct {
-	A [2]string
-}
-d := doc{}
-err := toml.Unmarshal([]byte(`A = ["one", "two", "many"]`), &d)
-fmt.Println(err)
-
-// (1, 1): unmarshal: TOML array length (3) exceeds destination array length (2)
-```
-
-In the same situation, v2 ignores the last value:
-
-```go
-err := toml.Unmarshal([]byte(`A = ["one", "two", "many"]`), &d)
-fmt.Println("err:", err, "d:", d)
-// err: <nil> d: {[one two]}
-```
-
-This is to match `encoding/json`'s behavior. There is no way to make the v2
-decoder behave like v1.
-
-#### Support for `toml.Unmarshaler` has been dropped
-
-This method was not widely used, poorly defined, and added a lot of complexity.
-A similar effect can be achieved by implementing the `encoding.TextUnmarshaler`
-interface and use strings.
-
-#### Support for `default` struct tag has been dropped
-
-This feature adds complexity and a poorly defined API for an effect that can be
-accomplished outside of the library.
-
-It does not seem like other format parsers in Go support that feature (the
-project referenced in the original ticket #202 has not been updated since 2017).
-Given that go-toml v2 should not touch values not in the document, the same
-effect can be achieved by pre-filling the struct with defaults (libraries like
-[go-defaults][go-defaults] can help). Also, string representation is not well
-defined for all types: it creates issues like #278.
-
-The recommended replacement is pre-filling the struct before unmarshaling.
-
-[go-defaults]: https://github.com/mcuadros/go-defaults
-
-#### `toml.Tree` replacement
-
-This structure was the initial attempt at providing a document model for
-go-toml. It allows manipulating the structure of any document, encoding and
-decoding from their TOML representation. While a more robust feature was
-initially planned in go-toml v2, this has been ultimately [removed from
-scope][nodoc] of this library, with no plan to add it back at the moment. The
-closest equivalent at the moment would be to unmarshal into an `interface{}` and
-use type assertions and/or reflection to manipulate the arbitrary
-structure. However this would fall short of providing all of the TOML features
-such as adding comments and be specific about whitespace.
-
-
-#### `toml.Position` are not retrievable anymore
-
-The API for retrieving the position (line, column) of a specific TOML element do
-not exist anymore. This was done to minimize the amount of concepts introduced
-by the library (query path), and avoid the performance hit related to storing
-positions in the absence of a document model, for a feature that seemed to have
-little use. Errors however have gained more detailed position
-information. Position retrieval seems better fitted for a document model, which
-has been [removed from the scope][nodoc] of go-toml v2 at the moment.
-
-### Encoding / Marshal
-
-#### Default struct fields order
-
-V1 emits struct fields order alphabetically by default. V2 struct fields are
-emitted in order they are defined. For example:
-
-```go
-type S struct {
-	B string
-	A string
-}
-
-data := S{
-	B: "B",
-	A: "A",
-}
-
-b, _ := tomlv1.Marshal(data)
-fmt.Println("v1:\n" + string(b))
-
-b, _ = tomlv2.Marshal(data)
-fmt.Println("v2:\n" + string(b))
-
-// Output:
-// v1:
-// A = "A"
-// B = "B"
-
-// v2:
-// B = 'B'
-// A = 'A'
-```
-
-There is no way to make v2 encoder behave like v1. A workaround could be to
-manually sort the fields alphabetically in the struct definition, or generate
-struct types using `reflect.StructOf`.
-
-#### No indentation by default
-
-V1 automatically indents content of tables by default. V2 does not. However the
-same behavior can be obtained using [`Encoder.SetIndentTables`][sit]. For example:
-
-```go
-data := map[string]interface{}{
-	"table": map[string]string{
-		"key": "value",
-	},
-}
-
-b, _ := tomlv1.Marshal(data)
-fmt.Println("v1:\n" + string(b))
-
-b, _ = tomlv2.Marshal(data)
-fmt.Println("v2:\n" + string(b))
-
-buf := bytes.Buffer{}
-enc := tomlv2.NewEncoder(&buf)
-enc.SetIndentTables(true)
-enc.Encode(data)
-fmt.Println("v2 Encoder:\n" + string(buf.Bytes()))
-
-// Output:
-// v1:
-//
-// [table]
-//   key = "value"
-//
-// v2:
-// [table]
-// key = 'value'
-//
-//
-// v2 Encoder:
-// [table]
-//   key = 'value'
-```
-
-[sit]: https://pkg.go.dev/github.com/pelletier/go-toml/v2#Encoder.SetIndentTables
-
-#### Keys and strings are single quoted
-
-V1 always uses double quotes (`"`) around strings and keys that cannot be
-represented bare (unquoted). V2 uses single quotes instead by default (`'`),
-unless a character cannot be represented, then falls back to double quotes. As a
-result of this change, `Encoder.QuoteMapKeys` has been removed, as it is not
-useful anymore.
-
-There is no way to make v2 encoder behave like v1.
-
-#### `TextMarshaler` emits as a string, not TOML
-
-Types that implement [`encoding.TextMarshaler`][tm] can emit arbitrary TOML in
-v1. The encoder would append the result to the output directly. In v2 the result
-is wrapped in a string. As a result, this interface cannot be implemented by the
-root object.
-
-There is no way to make v2 encoder behave like v1.
-
-[tm]: https://golang.org/pkg/encoding/#TextMarshaler
-
-#### `Encoder.CompactComments` has been removed
-
-Emitting compact comments is now the default behavior of go-toml. This option
-is not necessary anymore.
-
-#### Struct tags have been merged
-
-V1 used to provide multiple struct tags: `comment`, `commented`, `multiline`,
-`toml`, and `omitempty`. To behave more like the standard library, v2 has merged
-`toml`, `multiline`, `commented`, and `omitempty`. For example:
-
-```go
-type doc struct {
-	// v1
-	F string `toml:"field" multiline:"true" omitempty:"true" commented:"true"`
-	// v2
-	F string `toml:"field,multiline,omitempty,commented"`
-}
-```
-
-Has a result, the `Encoder.SetTag*` methods have been removed, as there is just
-one tag now.
-
-#### `Encoder.ArraysWithOneElementPerLine` has been renamed
-
-The new name is `Encoder.SetArraysMultiline`. The behavior should be the same.
-
-#### `Encoder.Indentation` has been renamed
-
-The new name is `Encoder.SetIndentSymbol`. The behavior should be the same.
-
-
-#### Embedded structs behave like stdlib
-
-V1 defaults to merging embedded struct fields into the embedding struct. This
-behavior was unexpected because it does not follow the standard library. To
-avoid breaking backward compatibility, the `Encoder.PromoteAnonymous` method was
-added to make the encoder behave correctly. Given backward compatibility is not
-a problem anymore, v2 does the right thing by default: it follows the behavior
-of `encoding/json`. `Encoder.PromoteAnonymous` has been removed.
-
-[nodoc]: https://github.com/pelletier/go-toml/discussions/506#discussioncomment-1526038
-
-### `query`
-
-go-toml v1 provided the [`go-toml/query`][query] package. It allowed to run
-JSONPath-style queries on TOML files. This feature is not available in v2. For a
-replacement, check out [dasel][dasel].
-
-This package has been removed because it was essentially not supported anymore
-(last commit May 2020), increased the complexity of the code base, and more
-complete solutions exist out there.
-
-[query]: https://github.com/pelletier/go-toml/tree/f99d6bbca119636aeafcf351ee52b3d202782627/query
-[dasel]: https://github.com/TomWright/dasel
-
 ## Versioning
 
 Expect for parts explicitly marked otherwise, go-toml follows [Semantic