message: Add caveat for covering features
  This section explains the caveats and possible solutions for features, detailing the tooling needed to 100% cover such a project.
  The need for this PR is based on a conversation with
  Moved this PR here based on comment:
diff: @@ -513,3 +513,9 @@ source and inspect it.
  [`cargo vendor`]: ../commands/cargo-vendor.md
  [cargo-clone-crate]: https://crates.io/crates/cargo-clone-crate
  +
  +### Caveats
  +
  +Features, which are a form of conditional compilation, require an exponential number of configurations and test cases to be 100% covered. By default, testing, linting, Miri, docs and others will only run on the default set of features.
  +
  +There are certain tools like [cargo-hack](https://github.com/taiki-e/cargo-hack) and [cargo-all-features](https://github.com/frewsxcv/cargo-all-features) that allow you to test all combinations of features which can help reduce the amount of configuraton needed.
  