Failed to load application files message improvement (#26214)

* Failed to load application files message improvement

* Apply suggestions from code review

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

public/views/index-template.html

@@ -199,7 +199,7 @@
         </p>
         <p>
           1. This could be caused by your reverse proxy settings.<br /><br />
-          2. If you host grafana under subpath make sure your grafana.ini root_url setting includes subpath<br />
+          2. If you host grafana under subpath make sure your grafana.ini root_url setting includes subpath. If not using a reverse proxy make sure to set serve_from_sub_path to true.<br />
           <br />
           3. If you have a local dev build make sure you build frontend using: yarn start, yarn start:hot, or yarn
           build<br />