First entries for 7.0 CHANGELOG

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

CHANGELOG

+v 7.0.0
+  - The CPU no longer overheats when you hold down the spacebar
+  - Improve edit file UI
+  - Add ability to upload group avatar when create
+
 v 6.9.0
   - Store Rails cache data in the Redis `cache:gitlab` namespace
   - Adjust MySQL limits for existing installations