Add deprecation notice

Change-Id: Ia38b491b8db170c55c64b923d07079ea0f59c1c6

README.md

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@@ -1,2 +1,8 @@
-# plugins_websession-broker
+# DEPRECATION NOTICE
+GerritForge has decided to [change the license to BSL](https://gitenterprise.me/2025/09/30/re-licensing-gerritforge-plugins-welcome-to-gerrit-enterprise/)
+therefore the Apache 2.0 version of this plugin is deprecated.
+The recommended version of the websession-broker plugin is on [GitHub](https://github.com/GerritForge/websession-broker)
+and the development continues on [GerritHub.io](https://review.gerrithub.io/admin/repos/GerritForge/websession-broker,general).
+
+# plugins_websession-broker (DEPRECATED)
 Gerrit Code Review plugin for storing and broadcasting websessions to an external broker