index.php: add upgrade script to migration section

index.php

@@ -751,6 +751,7 @@ function uri($uri) {
                         </div>
                         <hr>
                         <p>If you are using v1.0.0.rc4 or higher, <a href="./functions/upgrade100rc4.php">Click here</a> to upgrade your database to be compatible with v1.0.0.rc1 or higher, if created in a version lower than v1.0.0.rc1</p>
+                        <p>If you are using versions below 1.4.0 (and above 1.0.0rc4), click <a href="./functions/upgrade1.3.5to1.4.0.php">here</a> to upgrade your database.</p>
                     </div>
                     <br />
                     <button class="btn btn-secondary" data-toggle="collapse" href="#collapseAnno" role="button" aria-expanded="false" aria-controls="collapseAnno">Public Announcements</button>