message: Mention that cargo_metadata can parse json messages
diff: @@ -48,7 +48,11 @@ alter the way the JSON messages are computed and rendered. See the description
  of the `--message-format` option in the [build command documentation] for more
  details.
  +If you are using Rust, the [cargo_metadata] crate can be used to parse these
  +messages.
  +
  [build command documentation]: ../commands/cargo-build.md
  +[cargo_metadata]: https://crates.io/crates/cargo_metadata
  #### Compiler messages
  