Add entry to changelog

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.1.0 (unreleased)
+  - Add option to admin area to sign in as a specific user (Pavel Forkert)
   - Show CI status on all pages where commits list is rendered
   - Automatically enable CI when push .gitlab-ci.yml file to repository
   - Move CI charts to project graphs area