Merge branch 'ac-usage-quotas-docs' into 'master'

Document Usage Quotas group settings page

Closes #63022

See merge request gitlab-org/gitlab-ce!29599

doc/user/admin_area/settings/continuous_integration.md

@@ -89,10 +89,8 @@ are enabled.
 
 ![Project admin info](img/admin_project_quota_view.png)
 
-When the pipeline minutes quota for a group is set to a value different than 0,
-the **Pipelines quota** page is available to the group page settings list.
-You can see there an overview of the pipeline minutes quota of all projects of
-the group.
+You can see an overview of the pipeline minutes quota of all projects of
+a group in the **Usage Quotas** page available to the group page settings list.
 
 ![Group pipelines quota](img/group_pipelines_quota.png)
 

doc/user/group/index.md

@@ -381,6 +381,14 @@ Define project templates at a group level by setting a group as the template sou
   for the group. **[STARTER ONLY]**
 - **Pipelines quota**: Keep track of the [pipeline quota](../admin_area/settings/continuous_integration.md) for the group.
 
+#### Storage usage quota **[STARTER]**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/13294) in [GitLab Starter](https://about.gitlab.com/pricing/) 12.0.
+
+A group owner can check the aggregated storage usage for all the project in a group, sub-groups included, in the **Storage** tab of the **Usage Quotas** page available to the group page settings list.
+
+![Group storage usage quota](img/group_storage_usage_quota.png)
+
 ## User contribution analysis **[STARTER]**
 
 With [GitLab Contribution Analytics](contribution_analytics/index.md),