Merge branch 'epic-notifications' into 'master'

Link to notifications in epics

Closes #7651

See merge request gitlab-org/gitlab-ee!9839

doc/user/group/epics/index.md

@@ -205,3 +205,7 @@ Once you wrote your comment, you can either:
 ## Award emoji
 
 - You can [award an emoji](../../award_emojis.md) to that epic or its comments.
+
+## Notifications            
+
+- [Receive notifications](../../../workflow/notifications.md) for epic events.