message: Update README to reflect that the full git ref is not necessary
diff: @@ -93,7 +93,7 @@ on:
  description: The SHA-1 hash referring to the commit to check.
  required: true
  ref:
  - description: The full git ref for the PR (`refs/heads/my-branch`).
  + description: The head branch associated with the pull request.
  required: true
  ```
  