message: readme: fix broken link to `tokio-trace`
diff: @@ -37,7 +37,6 @@ merged to master.
  [`rev`]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#specifying-dependencies-from-git-repositories
  -
  ## Getting Help
  First, see if the answer to your question can be found in the API documentation.
  @@ -77,3 +76,5 @@ This project is licensed under the [MIT license](LICENSE).
  Unless you explicitly state otherwise, any contribution intentionally submitted
  for inclusion in Tokio by you, shall be licensed as MIT, without any additional
  terms or conditions.
  +
  +[`tokio-trace`]: https://github.com/tokio-rs/tokio/tree/master/tokio-trace
  