Add deprecation notice

Change-Id: I338c1ee8ff5244f8028da1c1c0213432b72060f2

README.md

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+# 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 analytics-etl plugin is on [GitHub](https://github.com/GerritForge/analytics-etl)
+and the development continues on [GerritHub.io](https://review.gerrithub.io/admin/repos/GerritForge/analytics-etl,general).
+
 # Intro
 
 This repository provides a set of spark ETL jobs able to extract, transform and persist data from