docs: add introduction to pandas users for adding columns with single text values (literal)

[ScottWilliamAnderson]

Description of changes

ibis generally follows pandas syntax for mutating columns, with the exception of adding string columns where ibis.literal is needed. ibis.literal is not mentioned yet in the pandas' user introductions, so it would be helpful to include this as it's not clear to the user why adding a float column or summing two columns together uses the same syntax as pandas, while a adding a single-valued string column does not.

This is the reason #11009 was opened (as a q&a link to send to new users).

Including it in the pandas introduction docs would reduce friction for switching to ibis for pandas users.

[github-actions]

ACTION NEEDED

Ibis follows the Conventional Commits specification for release automation.

The PR title and description are used as the merge commit message.

Please update your PR title and description to match the specification.

See https://github.com/ibis-project/ibis/blob/main/.releaserc.js
for the list of acceptable prefixes, eg "feat:", "fix:", "chore:", etc.

The commitlint output is:

npm warn exec The following package was not found and will be installed: [email protected]
⧗   input: Add introduction to pandas users for adding columns with single text values (literal)

## Description of changes

ibis generally follows pandas syntax for mutating columns, with the exception of adding string columns where `ibis.literal` is needed. `ibis.literal` is not mentioned yet in the pandas' user introductions, so it would be helpful to include this as it's not clear to the user why adding a float column or summing two columns together uses the same syntax as pandas, while a adding a single-valued string column does not. 

This is the reason https://github.com/ibis-project/ibis/discussions/11009 was opened (as a q&a link to send to new users).

Including it in the pandas introduction docs would reduce friction for switching to ibis for pandas users.
✖   subject may not be empty [subject-empty]
✖   type may not be empty [type-empty]

✖   found 2 problems, 0 warnings
ⓘ   Get help: https://github.com/conventional-changelog/commitlint/#what-is-commitlint

[ScottWilliamAnderson]

I think this is not needed, as recently the Getting Started docs now include introducing ibis.literal to the user:
#10918

[gforsyth]

Hey @ScottWilliamAnderson! I think having this info in multiple places is fine -- users coming from pandas might very well skip the "Getting Started" guide in favor of the "Coming from pandas" guide.

[ScottWilliamAnderson]

Hey @ScottWilliamAnderson! I think having this info in multiple places is fine -- users coming from pandas might very well skip the "Getting Started" guide in favor of the "Coming from pandas" guide.

Ah, great to hear. I've re-opened the PR, you can merge this if you find it helpful.

[gforsyth]

Thanks @ScottWilliamAnderson !