message: CONTRIBUTING.md: Update comment
diff: @@ -147,7 +147,7 @@ cd rustc
  cp config.toml.example config.toml
  # Now edit `config.toml` and set `debug-assertions = true`.
  -# Build a stage 1 rustc.
  +# Build a stage 1 rustc, and build the rustc libraries with that rustc.
  # This step can take 30 minutes or more.
  ./x.py build --stage 1 compiler/rustc
  # If you change something, you can get a faster rebuild by doing
  