Add docs for cherry-picking into a project

doc/user/project/merge_requests/cherry_pick_changes.md

@@ -9,7 +9,7 @@ type: reference, concepts
 
 GitLab implements Git's powerful feature to
 [cherry-pick any commit](https://git-scm.com/docs/git-cherry-pick "Git cherry-pick documentation")
-with introducing a **Cherry-pick** button in merge requests and commit details.
+with a **Cherry-pick** button in merge requests and commit details.
 
 ## Cherry-picking a merge request
 
@@ -60,6 +60,46 @@ mainline:
 git cherry-pick -m 2 7a39eb0
 ```
 
+### Cherry-pick into a project
+
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/21268) in GitLab 13.11.
+> - It's [deployed behind a feature flag](../../feature_flags.md), disabled by default.
+> - It's disabled on GitLab.com.
+> - It's not recommended for production use.
+> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-cherry-picking-into-a-project). **(FREE SELF)**
+
+WARNING:
+This feature might not be available to you. Check the **version history** note above for details.
+
+You can use the GitLab UI to cherry-pick merge requests into a project, even if the
+merge request is from a fork:
+
+1. In the merge request's secondary menu, click **Commits** to display the commit details page.
+1. Click on the **Options** dropdown and select **Cherry-pick** to show the cherry-pick modal.
+1. In **Pick into project** and **Pick into branch**, select the destination project and branch:
+   ![Cherry-pick commit](img/cherry_pick_into_project_v13_11.png)
+1. (Optional) Select **Start a new merge request** if you're ready to create a merge request.
+1. Click **Cherry-pick**.
+
+### Enable or disable cherry-picking into a project **(FREE SELF)**
+
+Cherry-picking into a project 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(:pick_into_project)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:pick_into_project)
+```
+
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues