- Document the release process in `CONTRIBUTING.md`
- Add development instructions to `CONTRIBUTING.md` (adapted from [download-artifact](https://github.com/actions/download-artifact))
- Add a test badge to the `README`
- Link to `CONTRIBUTING.md` in `README`
- Unify copy between `README.md` and `action.yml`
- Copy-pasta the CoC from [download-artifact](https://github.com/actions/download-artifact)