updated readme

Author: mike-parkhill

README.md

@@ -2,6 +2,9 @@
 ![license](https://img.shields.io/badge/License-Apache%202.0-blue?logo=apache&style=flat-square)
 [![maintainability](https://img.shields.io/codeclimate/maintainability-percentage/polkadot-js/apps?logo=code-climate&style=flat-square)](https://codeclimate.com/github/polkadot-js/apps)
 
+> [!NOTE]
+> The Dock blockchain has been closed. This project will no longer be maintained.
+
 # deployment
 `master` branch will deploy to fe.dock.io
 `dev` branch will deploy to fe-staging.dock.io