Link graphANNIS changelog

Author: thomaskrause

CHANGELOG.md

@@ -3,6 +3,8 @@
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+ANNIS is a frontend to the graphANNIS webservice, which has its [own changelog](https://github.com/korpling/graphANNIS/blob/main/CHANGELOG.md).
+
 ## [Unreleased]
 
 ## [4.15.1] - 2025-10-10