Changed message and title on the 404 page

changelogs/unreleased/add_message_to_the_404_page.yml

+---
+title: Changed message and title on the 404 page
+merge_request:
+author: Branka Martinovic
+type: added

public/404.html

@@ -72,8 +72,9 @@
     404
   </h1>
   <div class="container">
-    <h3>The page you're looking for could not be found.</h3>
+    <h3>This page could not be found or you don't have the permission.</h3>
     <hr />
+    <p>The resource that you are attempting to access does not exist or you don't have the necessary permissions to view it.</p>
     <p>Make sure the address is correct and that the page hasn't moved.</p>
     <p>Please contact your GitLab administrator if you think this is a mistake.</p>
     <a href="javascript:history.back()" class="js-go-back go-back">Go back</a>