message: Add a minor clarification
  Hopefully this will save the next person from wasting an hour+ on this.
diff: @@ -443,8 +443,7 @@ script specified with a custom library. The purpose of this functionality is to
  prevent running the build script in question altogether and instead supply the
  metadata ahead of time.
  -To override a build script, place the following configuration in any acceptable
  -Cargo [configuration location](config.md).
  +To override a build script, place the following configuration in any acceptable [`config.toml`](config.md) file.
  ```toml
  [target.x86_64-unknown-linux-gnu.foo]
  