Document how to enable Auto DevOps at the instance level

doc/user/admin_area/settings/continuous_integration.md

-# Continuous integration Admin settings
+# Continuous Integration and Deployment Admin settings **[CORE ONLY]**
 
-## Maximum artifacts size
+In this area, you will find settings for Auto DevOps, Runners and job artifacts.
+You can find it in the admin area, under **Settings > Continuous Integration and Deployment**.
 
-The maximum size of the [job artifacts][art-yml] can be set in the Admin area
-of your GitLab instance. The value is in *MB* and the default is 100MB. Note
-that this setting is set for each job.
-
-1. Go to **Admin area > Settings** (`/admin/application_settings`).
+![Admin area settings button](../img/admin_area_settings_button.png)
 
-    ![Admin area settings button](img/admin_area_settings_button.png)
+## Auto DevOps **[CORE ONLY]**
 
-1. Change the value of maximum artifacts size (in MB):
+To enable (or disable) [Auto DevOps](../../../topics/autodevops/index.md)
+for all projects:
 
-    ![Admin area maximum artifacts size](img/admin_area_maximum_artifacts_size.png)
+1. Go to **Admin area > Settings > Continuous Integration and Deployment**.
+1. Check (or uncheck to disable) the box that says "Default to Auto DevOps pipeline for all projects".
+1. Optionally, set up the [Auto DevOps base domain](../../../topics/autodevops/index.md#auto-devops-base-domain)
+   which is going to be used for Auto Deploy and Auto Review Apps.
+1. Hit **Save changes** for the changes to take effect.
 
-1. Hit **Save** for the changes to take effect.
+From now on, every existing project and newly created ones that don't have a
+`.gitlab-ci.yml`, will use the Auto DevOps pipelines.
 
-## Default artifacts expiration
+If you want to disable it for a specific project, you can do so in
+[its settings](../../../topics/autodevops/index.md#enabling-auto-devops).
 
-The default expiration time of the [job artifacts][art-yml] can be set in
-the Admin area of your GitLab instance. The syntax of duration is described
-in [artifacts:expire_in][duration-syntax]. The default is `30 days`. Note that
-this setting is set for each job. Set it to `0` if you don't want default
-expiration. The default unit is in seconds.
+## Maximum artifacts size **[CORE ONLY]**
 
+The maximum size of the [job artifacts][art-yml] can be set in the Admin area
+of your GitLab instance. The value is in *MB* and the default is 100MB per job;
+on GitLab.com it's [set to 1G](../../gitlab_com/index.md#gitlab-ci-cd).
 
-1. Go to **Admin area > Settings** (`/admin/application_settings`).
+To change it:
 
-    ![Admin area settings button](img/admin_area_settings_button.png)
+1. Go to **Admin area > Settings > Continuous Integration and Deployment**.
+1. Change the value of maximum artifacts size (in MB).
+1. Hit **Save changes** for the changes to take effect.
 
-1. Change the value of default expiration time ([syntax][duration-syntax]):
+## Default artifacts expiration **[CORE ONLY]**
 
-    ![Admin area default artifacts expiration](img/admin_area_default_artifacts_expiration.png)
+The default expiration time of the [job artifacts](../../../administration/job_artifacts.md)
+can be set in the Admin area of your GitLab instance. The syntax of duration is
+described in [`artifacts:expire_in`](../../../ci/yaml/README.md#artifacts-expire_in)
+and the default value is `30 days`. On GitLab.com they
+[never expire](../../gitlab_com/index.md#gitlab-ci-cd).
 
-1. Hit **Save** for the changes to take effect.
+1. Go to **Admin area > Settings > Continuous Integration and Deployment**.
+1. Change the value of default expiration time.
+1. Hit **Save changes** for the changes to take effect.
 
-[art-yml]: ../../../administration/job_artifacts.md
-[duration-syntax]: ../../../ci/yaml/README.md#artifactsexpire_in
+This setting is set per job and can be overridden in
+[`.gitlab-ci.yml`](../../../ci/yaml/README.md#artifacts-expire_in).
+To disable the expiration, set it to `0`. The default unit is in seconds.

doc/user/admin_area/settings/index.md

+# Admin area settings **[CORE ONLY]**
+
+In the admin area settings, you can find various options for your GitLab
+instance like sign-up restrictions, account limits and quota, metrics, etc.
+
+Navigate to it by going to **Admin area > Settings**. Some of the settings
+include:
+
+- [Continuous Integration and Deployment](continuous_integration.md)
+- [Email](email.md)
+- [Sign up restrictions](sign_up_restrictions.md)
+- [Terms](terms.md)
+- [Third party offers](third_party_offers.md)
+- [Usage statistics](usage_statistics.md)
+- [Visibility and access controls](visibility_and_access_controls.md)
+
+## GitLab.com admin area settings
+
+Most of the settings under the admin area change the behavior of the whole
+GitLab instance. For GitLab.com, the admin settings are available only for the
+GitLab.com administrators, and the parameters can be found on the
+[GitLab.com settings](../../gitlab_com/index.md) documentation.