Prepare repo for archive

Author: Sarah Edwards

README.md

@@ -1,10 +1,12 @@
-This is an example GitHub App that adds a label to all new issues opened in a repository. You can follow the "[Using the GitHub API in your app](https://developer.github.com/apps/quickstart-guides/using-the-github-api-in-your-app/)" quickstart guide on developer.github.com to learn how to build the app code in `server.rb`.
+⚠️ Note: This repository is not maintained. For more recent guides about how to build GitHub Apps, see "[About writing code for a GitHub App](https://docs.github.com/en/apps/creating-github-apps/writing-code-for-a-github-app/about-writing-code-for-a-github-app)."
+
+This is an example GitHub App that adds a label to all new issues opened in a repository. You can follow the archived "[Using the GitHub API in your app](https://web.archive.org/web/20230604175646/https://docs.github.com/en/apps/creating-github-apps/writing-code-for-a-github-app/using-the-github-api-in-your-app)" guide to learn how to build the app code in `server.rb`.
 
 This project listens for webhook events and uses the Octokit.rb library to make REST API calls. This example project consists of two different servers:
 * `template_server.rb` (GitHub App template code)
 * `server.rb` (completed project)
 
-To learn how to set up a template GitHub App, follow the "[Setting up your development environment](https://developer.github.com/apps/quickstart-guides/setting-up-your-development-environment/)" quickstart guide on developer.github.com.
+To learn how to set up a template GitHub App, follow the archived "[Setting up your development environment](https://web.archive.org/web/20230604175646/https://docs.github.com/en/apps/creating-github-apps/writing-code-for-a-github-app/setting-up-your-development-environment-to-create-a-github-app)" guide.
 
 ## Install