DEV: Deprecate the plugin (#281)

Author: cvx

README.md

@@ -1,5 +1,8 @@
 # Discourse Subscriptions Plugin
 
+> [!IMPORTANT]
+> This plugin has now been bundled into Discourse core. See: https://meta.discourse.org/t/bundling-more-popular-plugins-with-discourse-core/373574
+
 Discourse Subscriptions allows site owners to sell recurring and one-time purchase subscriptions that grant access to a group on a Discourse instance.
 
 For more information, please see: https://meta.discourse.org/t/discourse-subscriptions-plugin/140818