Add missing changelog item about improving navigation sidebar

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

CHANGELOG

@@ -18,6 +18,7 @@ v 8.7.0 (unreleased)
   - Fix creation of merge requests for orphaned branches (Stan Hu)
   - Fall back to `In-Reply-To` and `References` headers when sub-addressing is not available (David Padilla)
   - Remove "Congratulations!" tweet button on newly-created project. (Connor Shea)
+  - Improved UX of the navigation sidebar
 
 v 8.6.4
   - Don't attempt to fetch any tags from a forked repo (Stan Hu)