Changelog: note Sync client helper and builder changes

Author: greenrobot-team

CHANGELOG.md

@@ -9,6 +9,13 @@ For more insights into what changed in the ObjectBox C++ core, [check the Object
 - The [ObjectBox Gradle plugin](https://github.com/objectbox/objectbox-java-generator) requires JDK 11 and Android
   Gradle Plugin 8.1 or newer.
 
+### Sync
+
+- Add simplified `Sync.client(boxStore)` helper method. Move URL and credentials options to builder, add variants that 
+  accept multiple URLs and credentials. Deprecate the existing helper methods.
+- Add Sync client builder option to configure Sync behavior using 
+  [SyncFlags](objectbox-java/src/main/java/io/objectbox/sync/SyncFlags.java).
+
 ## 5.1.0 - 2026-01-26
 
 - Add [ObjectBoxThreadPoolExecutor](objectbox-java/src/main/java/io/objectbox/ObjectBoxThreadPoolExecutor.java), a