docs: 📚️ action options

Author: bubkoo

README.md

@@ -4,7 +4,7 @@ This GitHub Action can be used to impersonate a GitHub App when `secrets.GITHUB_
 
 [`secrets.GITHUB_TOKEN`](https://help.github.com/en/actions/configuring-and-managing-workflows/authenticating-with-the-github_token) has limitations such as [not being able to triggering a new workflow from another workflow](https://github.community/t5/GitHub-Actions/Triggering-a-new-workflow-from-another-workflow/td-p/31676). A workaround is to use a [personal access token](https://help.github.com/en/github/authenticating-to-github/creating-a-personal-access-token-for-the-command-line) from a [personal user/bot account](https://help.github.com/en/github/getting-started-with-github/types-of-github-accounts#personal-user-accounts). However, for organizations, GitHub Apps are [a more appropriate automation solution](https://developer.github.com/apps/differences-between-apps/#machine-vs-bot-accounts).
 
-# Example Workflow
+## Example Workflow
 
 ```yml
 jobs:
@@ -23,3 +23,15 @@ jobs:
         run: |
           echo "The generated token is masked: ${TOKEN}"
 ```
+
+### Options
+
+- `APP_ID`: The ID of the GitHub App.
+- `PRIVATE_KEY`: The private key of the GitHub App (can be Base64 encoded).
+- `VARIABLE_NAME`: The name of generated token in exported variable. Specify a varable name will set an environment variable with specfiied name and valued with generated token, and can be use in next step with `${ VARIABLE_NAME }`.
+- `SECRET_NAME`: The secret name created on current repository. Specify a secret name will add an secret on current repository with specfiied name and valued with generated token and can be use in next step with `${{ secrets.SECRET_NAME }}`.
+- `CLEAN_SECRET`: Shoule clean the secret or not when the job completed. Only used when `SECRET_NAME` specfiied. Default `false`.
+
+## License
+
+The scripts and documentation in this project are released under the [MIT License](LICENSE)