Document how to enable Dependency Scanning via an MR

Document how DS can be enabled via an automatically created MR from the
Security Configuration page.

doc/user/application_security/configuration/index.md

@@ -78,6 +78,9 @@ You can configure the following security controls:
 - Secret Detection
   - Select **Configure via Merge Request** to create a merge request with the changes required to
     enable Secret Detection. For more details, see [Enable Secret Detection via an automatic merge request](../secret_detection/index.md#enable-secret-detection-via-an-automatic-merge-request).
+- Dependency Scanning
+  - Select **Configure via Merge Request** to create a merge request with the changes required to
+    enable Dependency Scanning. For more details, see [Enable Dependency Scanning via an automatic merge request](../dependency_scanning/index.md#enable-dependency-scanning-via-an-automatic-merge-request).
 
 ## Enable or disable UI redesign **(FREE SELF)**
 

doc/user/application_security/dependency_scanning/index.md

@@ -110,6 +110,27 @@ The results are saved as a
 that you can later download and analyze. Due to implementation limitations, we
 always take the latest dependency scanning artifact available.
 
+### Enable Dependency Scanning via an automatic merge request
+
+> - [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/4908) in GitLab 13.11.
+> - [Deployed behind a feature flag](../../../user/feature_flags.md), disabled by default.
+> - Disabled on GitLab.com.
+> - Not recommended for production use.
+> - To use in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-configure-dependency-scanning-via-a-merge-request).
+
+WARNING:
+This feature might not be available to you. Check the **version history** note above for details.
+
+If Dependency Scanning isn't yet enabled in your project, you can automatically create a merge request
+from the Security Configuration page.
+
+1. In the project where you want to enable Dependency Scanning, navigate to
+   **Security & Compliance > Configuration**.
+1. In the **Dependency Scanning** row, select **Configure via Merge Request**.
+
+This automatically creates a merge request with the changes necessary to enable Dependency Scanning
+that you can review and merge to complete the configuration.
+
 ### Customizing the dependency scanning settings
 
 The dependency scanning settings can be changed through [CI/CD variables](#available-cicd-variables) by using the
@@ -656,3 +677,22 @@ with a dependency on this version of Python should use `retire.js` version 2.10.
 ### Error: `dependency_scanning is used for configuration only, and its script should not be executed`
 
 For information on this, see the [GitLab Secure troubleshooting section](../index.md#error-job-is-used-for-configuration-only-and-its-script-should-not-be-executed).
+
+### Enable or disable Configure Dependency Scanning via a Merge Request
+
+Configure Dependency Scanning via a Merge Request is under development and not ready for production use. It is
+deployed behind a feature flag that is **disabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
+can enable it.
+
+To enable it:
+
+```ruby
+Feature.enable(:sec_dependency_scanning_ui_enable)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:sec_dependency_scanning_ui_enable)
+```