Prepare changelog for v1.5.6

Author: RiotRobot

CHANGELOG.md

@@ -1,3 +1,9 @@
+Changes in [1.5.6](https://github.com/vector-im/riot-web/releases/tag/v1.5.6) (2019-12-09)
+==========================================================================================
+[Full Changelog](https://github.com/vector-im/riot-web/compare/v1.5.6-rc.1...v1.5.6)
+
+ * No changes since rc.1
+
 Changes in [1.5.6-rc.1](https://github.com/vector-im/riot-web/releases/tag/v1.5.6-rc.1) (2019-12-04)
 ====================================================================================================
 [Full Changelog](https://github.com/vector-im/riot-web/compare/v1.5.5...v1.5.6-rc.1)