Clarify the docs review process and mention the supported repos

doc/development/writing_documentation.md

@@ -152,12 +152,23 @@ CE and EE.
 ## Previewing the changes live
 
 If you want to preview the doc changes of your merge request live, you can use
-the manual `review-docs-deploy` job in your merge request.
+the manual `review-docs-deploy` job in your merge request. You will need at
+least Master permissions to be able to run it and is currently enabled for the
+following projects:
+
+- https://gitlab.com/gitlab-org/gitlab-ce
+- https://gitlab.com/gitlab-org/gitlab-ee
+
+NOTE: **Note:**
+You will need to push a branch to those repositories, it doesn't work for forks.
 
 TIP: **Tip:**
 If your branch contains only documentation changes, you can use
 [special branch names](#testing) to avoid long running pipelines.
 
+In the mini pipeline graph, you should see an `>>` icon. Clicking on it will
+reveal the `review-docs-deploy` job. Hit the play button for the job to start.
+
 ![Manual trigger a docs build](img/manual_build_docs.png)
 
 This job will: