docs: document client ID support for app-id

Co-authored-by: parkerbxyz <17183625+parkerbxyz@users.noreply.github.com>

README.md

@@ -9,9 +9,11 @@ GitHub Action for creating a GitHub App installation access token.
 In order to use this action, you need to:
 
 1. [Register new GitHub App](https://docs.github.com/apps/creating-github-apps/setting-up-a-github-app/creating-a-github-app).
-2. [Store the App's ID or Client ID in your repository environment variables](https://docs.github.com/actions/learn-github-actions/variables#defining-configuration-variables-for-multiple-workflows) (example: `APP_ID`).
+2. [Store the App's Client ID (recommended) or App ID in your repository environment variables](https://docs.github.com/actions/learn-github-actions/variables#defining-configuration-variables-for-multiple-workflows) (example: `APP_ID`).
 3. [Store the App's private key in your repository secrets](https://docs.github.com/actions/security-guides/encrypted-secrets?tool=webui#creating-encrypted-secrets-for-a-repository) (example: `PRIVATE_KEY`).
 
+Pass the App's Client ID or App ID using the `app-id` input. GitHub recommends using the Client ID when available.
+
 > [!IMPORTANT]  
 > An installation access token expires after 1 hour. Please [see this comment](https://github.com/actions/create-github-app-token/issues/121#issuecomment-2043214796) for alternative approaches if you have long-running processes.
 
@@ -318,7 +320,7 @@ If you set `HTTP_PROXY` or `HTTPS_PROXY`, also set `NODE_USE_ENV_PROXY: "1"` on
 
 ### `app-id`
 
-**Required:** GitHub App ID.
+**Required:** GitHub App Client ID or App ID. GitHub recommends using the Client ID when available.
 
 ### `private-key`