message: Fix broken link in reference docs
diff: @@ -113,6 +113,7 @@ supported environment variables are:
  [`cargo install`]: ../commands/cargo-install.md
  [`cargo new`]: ../commands/cargo-new.md
  [`cargo rustc`]: ../commands/cargo-rustc.md
  +[`cargo rustdoc`]: ../commands/cargo-rustdoc.md
  [config-env]: config.md#environment-variables
  [crates.io]: https://crates.io/
  [incremental compilation]: profiles.md#incremental
  