Add Open in Xcode docs

doc/user/project/repository/index.md

@@ -176,4 +176,12 @@ Lock your files to prevent any conflicting changes.
 
 You can access your repos via [repository API](../../../api/repositories.md).
 
+## Clone in Apple Xcode
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/45820) in GitLab 11.0
+
+Projects that contain a `.xcodeproj` or `.xcworkspace` file can now be cloned
+in Xcode using the new **Open in Xcode** button, located next to the Git URL
+used for cloning your project. The button is only shown on MacOS.
+
 [jupyter]: https://jupyter.org