Add to member lock to changelog and documentation.

CHANGELOG-EE

@@ -2,6 +2,7 @@ v 7.6.0
   - Added Audit events related to membership changes for groups and projects
   - Added option to attempt a rebase before merging merge request
   - Dont show LDAP groups settings if LDAP disabled
+  - Added member lock for groups to disallow membership changes on project level
 
 v 7.5.3
   - Only set up Sidetiq from a Sidekiq server process (fixes Redis::InheritedError)

doc/workflow/groups.md

@@ -69,3 +69,16 @@ gitlab_rails['gitlab_default_can_create_group'] = false
 # For installations from source, uncomment the 'default_can_create_group'
 # line in /home/git/gitlab/config/gitlab.yml
 ```
+
+## Lock project membership to members of the group
+
+In GitLab Enterprise Edition it is possible to lock membership in project to the level of members in group.
+
+This allows group owner to lock down any new project membership to any of the projects within the group allowing tighter control over
+project membership.
+
+To enable this feature, navigate to group settings page, select `Member lock` and `Save group`.
+
+![Checkbox for membership lock](groups/membership_lock.png)
+
+This will disable the option for all users who previously had permissions to operate project memberships. No new users can be added, removed or their access level changed. Furthermore, any request to change project permission level for users through API will not be possible.