chore: add archive notice (#20)

* add archive notice

* update-heading

Author: JEverhart383

README.md

@@ -1,5 +1,10 @@
 # **Knock + Node.js example app**
 
+## Archive notice
+As of March 2024, this repository has been moved to a read-only archive. It's still usable and contains useful information, but we'll be porting this application to a newer version of Next.js in the very near future. In the meantime, you can check out the [example apps section](https://docs.knock.app/getting-started/example-app) of the Knock docs for a list of our example apps.
+
+## About
+
 This example app uses [Knock](https://knock.app) to power cross channel notifications via email, an in-app feed, and Slack inside of a full-stack Node application, written in [Blitz.js](https://blitzjs.com/). It uses the [Knock Node SDK](https://github.com/knocklabs/knock-node) and [React in-app feed components](https://github.com/knocklabs/react-notification-feed).
 
 You can read more about this example app [in the Knock documentation](https://docs.knock.app/getting-started/example-app#nodejs-example-app).