Address more review comments in rust-lang#1286.

Author: nnethercote

src/doc/rustc-dev-guide/src/building/how-to-build-and-run.md

@@ -182,7 +182,7 @@ You almost never need to do this.
 
 If you are working on the standard library, you probably don't need to build
 the compiler unless you are planning to use a recently added nightly feature.
-Instead, you can just build stage 0, which uses the current beta compiler.
+Instead, you can just build using the bootstrap compiler.
 
 ```bash
 ./x.py build --stage 0 library/std

src/doc/rustc-dev-guide/src/rustdoc.md

@@ -42,7 +42,7 @@ does is call the `main()` that's in this crate's `lib.rs`, though.)
 * Run `./x.py setup tools` before getting started. This will configure `x.py`
   with nice settings for developing rustdoc and other tools, including
   downloading a copy of rustc rather than building it.
-* Use `./x.py check` to quickly check for compile errors.
+* Use `./x.py check src/tools/rustdoc` to quickly check for compile errors.
 * Use `./x.py build` to make a usable
   rustdoc you can run on other projects.
   * Add `library/test` to be able to use `rustdoc --test`.