Improve github actions documentation

Check if the github actions api is fully documented and check if the `$parameters` options array is documented.

Start by locating the GitHub Actions API documentation and the `$parameters` options array in the project. Compare the available API coverage and parameter options with the existing documentation. Done means the Actions API and the `$parameters` options are fully documented; no specific files or tests are named in the issue.

索引モデルが issue の本文から書いたものです。