Add canonical README.yaml for CI-generated README.md

[Copilot]

This PR introduces a canonical README.yaml so README.md can be generated in CI using the repository-standard Cloud Posse docs workflow. The content mirrors the current action behavior and usage while aligning format with sibling Cloud Posse action repos.

• Canonical README source

  • Adds README.yaml at repo root as the single source of truth for generated documentation.
  • Defines standard metadata fields (name, tags, license, github_repo, badges, related, include, contributors).

• Action-focused documentation content

  • Captures concise project description and introduction for github-action-pre-commit.
  • Adds usage examples for:
    • default action invocation
    • custom extra_args
    • private-repo push-back configuration (token, git author, commit message).

• Cloud Posse README.yaml convention alignment

  • Uses the same structure and section model as referenced Cloud Posse action repositories.
  • Includes reusable workflow reference links and badge format consistent with the org pattern.

# README.yaml (excerpt)
name: github-action-pre-commit
github_repo: cloudposse/github-action-pre-commit

usage: |-
  ```yaml
  - uses: cloudposse/github-action-pre-commit@v4.0.0
    with:
      token: ${{ secrets.GITHUB_TOKEN }}
      git_user_name: pre-commit
      git_user_email: pre-commit@users.noreply.github.com
      git_commit_message: pre-commit fixes

[github-actions]

These changes were released in v4.1.0.