Add documentation for 'Share with groups'

doc/workflow/README.md

@@ -2,3 +2,4 @@
 - [Project Features](project_features.md)
 - [Authorization for merge requests](authorization_for_merge_requests.md)
 - [Groups](groups.md)
+- [Share projects with other groups](share_projects_with_other_groups.md)

doc/workflow/share_projects_with_groups.md

+# Share Projects with Groups
+
+In GitLab Enterprise Edition you can share projects with groups.
+This makes it possible to add a group of users to a project with a single action.
+
+## Groups as collections of users
+
+In GitLab Community Edition groups are used primarily to [create collections of projects](groups.md).
+In GitLab Enterprise Edition you can also take advantage of the fact that groups define collections of _users_, namely the group members.
+
+## Sharing a project with a group of users
+
+The primary mechanism to give a group of users, say 'Engineering', access to a project, say 'Project Acme', in GitLab is to make the 'Engineering' group the owner of 'Project Acme'.
+But what if 'Project Acme' already belongs to another group, say 'Open Source'?
+This is where the (Enterprise Edition only) group sharing feature can be of use.
+
+To share 'Project Acme' with the 'Engineering' group, go to the project settings page for 'Project Acme' and use the left navigation menu to go to the 'Groups' section.
+
+![The 'Groups' section in the project settings screen (Enterprise Edition only)](groups/share_project_with_groups.png)
+
+Now you can add the Engineering group with the maximum access level of your choice.
+
+![Now 'Project Acme' is shared with 'Engineering' with a maximum access level of 'Developer'](groups/max_access_level.png)
+
+The maximum access level of 'Developer' for members from 'Engineering' means that users with higher access levels in 'Engineering' ('Master' or 'Owner') will only have 'Developer' access to 'Project Acme'.