service/blog: clarify what happens with forks

service/blog.md

@@ -22,8 +22,13 @@ should still be created to allow the review process to occur.
   * We'll create a new branch in the repository, so your account will require
     `Developper` permissions in the project
 
-  * If you're missing the permissions, please ask TPA. Opening a Merge Request
-    from a personal fork will cause CI to fail to deploy the preview
+  * If you're missing the permissions, please ask TPA.
+
+  * If you choose to fork the project in your personal GitLab namespace, CI will
+    instead deploy the build to GitLab Pages, and the `View app` button described
+    below will not appear on the Merge Request page. In this case, to view the
+    build, open the fork project and open `Settings` -> `Pages` and click the URL
+    under `Access pages`.
 
 #### 2. Click the `Web IDE` button just above the file listing