Mention performance improvements after adding cache to some fragments

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

CHANGELOG

@@ -26,6 +26,7 @@ v 7.13.0 (unreleased)
   - Improve performance for issue and merge request pages 
   - Users with guest access level can not set assignee, labels or milestones for issue and merge request
   - Reporter role can manage issue tracker now: edit any issue, set assignee or milestone and manage labels
+  - Better performance for pages with events list, issues list and commits list
 v 7.12.0
   - Fix Error 500 when one user attempts to access a personal, internal snippet (Stan Hu)