Add UI changes in 8.8 to changelog

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

CHANGELOG

@@ -49,6 +49,8 @@ v 8.8.0 (unreleased)
   - Total method execution timings are no longer tracked
   - Allow Admins to remove the Login with buttons for OAuth services and still be able to import !4034. (Andrei Gliga)
   - Add API endpoints for un/subscribing from/to a label. !4051 (Ahmad Sherif)
+  - Hide left sidebar on phone screens to give more space for content
+  - Redesign navigation for profile and group pages
 
 v 8.7.5
   - Fix relative links in wiki pages. !4050