Add deprecation notice to readme

readme.txt

@@ -8,6 +8,11 @@ Stable tag: 11.6.2
 License: GPLv3
 License URI: https://www.gnu.org/licenses/gpl-3.0.html
 
+== This Plugin is Deprecated ==
+As of December 2023, we [merged the standalone WooCommerce Blocks plugin into WooCommerce itself](https://developer.woo.com/2023/12/11/the-woo-blocks-merge-to-the-monorepo-is-complete-along-with-monorepo-tool-enhancements/). All future development will now take place directly in WooCommerce.
+
+If you're building Blocks-based functionality for WooCommerce, you no longer need this plugin.
+
 == Description ==
 
 WooCommerce Blocks are the easiest, most flexible way to display your products on posts and pages!