Metadata syntax for GitHub Actions
Docker and JavaScript actions require a metadata file. The metadata filename must be either action.yml or action.yaml. The data in the metadata file defines the inputs, outputs and main entrypoint for your action. Action metadata files use YAML syntax. If you're new to YAML, you can read " Learn YAML in five minutes."
https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#about-yaml-syntax-for-github-actions
