Add documentation around auditor users.

doc/README.md

@@ -77,6 +77,7 @@
 - [High Availability](administration/high_availability/README.md) Configure multiple servers for scaling or high availability.
 - [Container Registry](administration/container_registry.md) Configure Docker Registry with GitLab.
 - [Repository restrictions](user/admin_area/settings/account_and_limit_settings.md#repository-size-limit) Define size restrictions for your repositories to limit the space they occupy in your storage device. Includes LFS objects.
+- [Auditor users](administration/auditor_users.md) Create auditor users, with read-only access to the entire system.
 
 ## Contributor documentation
 

doc/administration/auditor_users.md

+# Auditor Users
+
+>**Note:** [Introduced][998] in GitLab 8.16.
+
+With Gitlab Enterprise Edition Premium, you can create *auditor* users, who 
+are given read-only access to all projects, groups, and other resources on the 
+GitLab instance.
+
+First and foremost, an auditor user can perform all the actions that a regular user can.
+In projects that the auditor user owns, or has been added to, they can be added to
+groups, mentioned in comments, or have issues assigned to them. The one exception is 
+that auditor users cannot _create_ projects or groups.
+
+In addition, the auditor will be granted read-only access to all other projects/groups/etc.
+on the GitLab instance.
+
+The `auditor` role is _not_ a read-only version of the `admin` role. The auditor will not be
+able to access the project settings pages, or the Admin Area.
+
+[998]: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/998