Add CI Badge

[ScottGibb]

Simple PR for adding a badge to the markdown indicating the Clippy tests and formats.

Couple of questions that may be worth thinking about (small things)

• In https://github.com/embassy-rs/trouble the test CI is called ci.yaml, where as this one is called check.yml. Do we want to standardise this across the two repos?

[alexmoon]

Thanks, but I don’t think a CI badge adds any value for this project. Our policy is not to merge PRs unless CI passes.

[ScottGibb]

No worries :) Is it possible to add a description to the GitHub Repo "about" section, I don't have access to do it on my end.