message: Add some tracking issues to unstable docs.
diff: @@ -1236,6 +1236,7 @@ rust-version = "1.42"
  ```
  ### edition 2021
  +* Tracking Issue: [rust-lang/rust#85811](https://github.com/rust-lang/rust/issues/85811)
  Support for the 2021 [edition] can be enabled by adding the `edition2021`
  unstable feature to the top of `Cargo.toml`:
  @@ -1281,6 +1282,7 @@ developers of the dependencies to help resolve the issue.
  ### configurable-env
  * Original Pull Request: [#9175](https://github.com/rust-lang/cargo/pull/9175)
  +* Tracking Issue: [#9539](https://github.com/rust-lang/cargo/issues/9539)
  The `-Z configurable-env` flag enables the `[env]` section in the
  `.cargo/config.toml` file. This section allows you to set additional environment
  