message: Mention `cargo metadata` for custom subcommands.
diff: @@ -241,5 +241,11 @@ Cargo. Alternatively, it can link to `cargo` crate as a library, but this
  approach has drawbacks:
  * Cargo as a library is unstable: the API may change without deprecation
  -
  * versions of the linked Cargo library may be different from the Cargo binary
  +
  +Instead, it is encouraged to use the CLI interface to drive Cargo. The [`cargo
  +metadata`] command can be used to obtain information about the current project
  +(the [`cargo_metadata`] crate provides a Rust interface to this command).
  +
  +[`cargo metadata`]: ../commands/cargo-metadata.md
  +[`cargo_metadata`]: https://crates.io/crates/cargo_metadata
  