Bring share with group feature documentation from EE

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

doc/workflow/README.md

@@ -13,6 +13,8 @@
 - [Project forking workflow](forking_workflow.md)
 - [Project users](add-user/add-user.md)
 - [Protected branches](protected_branches.md)
+- [Sharing a project with a group](share_with_group.md)
+- [Share projects with other groups](share_projects_with_other_groups.md)
 - [Web Editor](web_editor.md)
 - [Releases](releases.md)
 - [Milestones](milestones.md)

doc/workflow/share_projects_with_other_groups.md

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+# Share Projects with other Groups
+
+In GitLab Enterprise Edition you can share projects with other 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.
+After sharing 'Project Acme' with 'Engineering', the project is listed on the group dashboard.
+
+!['Project Acme' is listed as a shared project for 'Engineering'](groups/other_group_sees_shared_project.png)
+
+## Maximum access level
+
+!['Project Acme' is shared with 'Engineering' with a maximum access level of 'Developer'](groups/max_access_level.png)
+
+In the screenshot above, 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'.

doc/workflow/share_with_group.md

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+# Sharing a project with a group
+
+If you want to share a single project in a group with another group,
+you can do so easily. By setting the permission you can quickly
+give a select group of users access to a project in a restricted manner.
+
+In a project go to the project settings -> groups.
+
+Now you can select a group that you want to share this project with and with
+which maximum access level. Users in that group are able to access this project
+with their set group access level, up to the maximum level that you've set.
+
+![Share a project with a group](share_with_group.png)