Merge branch 'docs/add-admin-area-index-ee' into 'master'

Add an index page to admin area section

See merge request gitlab-org/gitlab-ee!9601

doc/administration/index.md

@@ -62,6 +62,7 @@ Learn how to install, configure, update, and maintain your GitLab instance.
 - [Elasticsearch](../integration/elasticsearch.md): Enable Elasticsearch to empower GitLab's Advanced Global Search. Useful when you deal with a huge amount of data. **[STARTER ONLY]**
 - [External Classification Policy Authorization](../user/admin_area/settings/external_authorization.md) **[PREMIUM ONLY]**
 - [Upload a license](../user/admin_area/license.md): Upload a license to unlock features that are in paid tiers of GitLab. **[STARTER ONLY]**
+- [Admin Area](../user/admin_area/index.md): for self-managed instance-wide configuration and maintenance.
 
 #### Customizing GitLab's appearance
 

doc/user/admin_area/geo_nodes.md

-# Geo nodes admin area
+# Geo nodes admin area **[PREMIUM ONLY]**
 
 For more information about setting up GitLab Geo, read the
 [Geo documentation](../../gitlab-geo/README.md).

doc/user/admin_area/index.md

+# GitLab Admin Area **[CORE ONLY]**
+
+The Admin Area provides a web UI for administering some features of GitLab self-managed instances.
+
+To access the Admin Area, either:
+
+- Click the Admin Area icon (the spanner or wrench icon).
+- Visit `/admin` on your self-managed instance.
+
+NOTE: **Note:**
+Only admin users can access the Admin Area.
+
+## Admin Area sections
+
+The Admin Area is made up of the following sections:
+
+| Section                    | Description                                                                                                                                              |
+|:---------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Overview                   | View your GitLab Dashboard, and maintain projects, users, groups, jobs, runners, and Gitaly servers.                                                     |
+| Monitoring                 | View GitLab system information, and information on background jobs, logs, [health checks](monitoring/health_check.md), request profiles, and audit logs. |
+| Messages                   | Send and manage [broadcast messages](broadcast_messages.md) for your users.                                                                              |
+| System Hooks               | Configure [system hooks](../../system_hooks/system_hooks.md) for many events.                                                                            |
+| Applications               | Create system [OAuth applications](../../integration/oauth_provider.md) for integrations with other services.                                            |
+| Abuse Reports              | Manage [abuse reports](abuse_reports.md) submitted by your users.                                                                                        |
+| License **[STARTER ONLY]** | Upload, display, and remove [licenses](license.md).                                                                                                      |
+| Push Rules **[STARTER]**   | Configure pre-defined git [push rules](../../push_rules/push_rules.md) for projects.                                                                                |
+| Geo **[PREMIUM ONLY]**     | Configure and maintain [Geo nodes](geo_nodes.md).                                                                                                        |
+| Deploy Keys                | Create instance-wide [SSH deploy keys](../../ssh/README.md#deploy-keys).                                                                                 |
+| Service Templates          | Create [service templates](../project/integrations/services_templates.md) for projects.                                                                  |
+| Labels                     | Create and maintain [labels](labels.md) for your GitLab instance.                                                                                        |
+| Appearance                 | Customize [GitLab's appearance](../../customization/index.md).                                                                                           |
+| Settings                   | Modify the [settings](settings/index.md) for your GitLab instance.                                                                                       |