Documentation: Add information about fix_quiz_id_to_iid.php for installs previous to 1.11.0.

documentation/installation_guide.html

@@ -331,6 +331,13 @@ As this is only a minor version change from previous 1.11.* versions of Chamilo,
       You can also delete the contents of this directory through the "Cleanup of cache and temporary files " option in the "System" box of the Administration page.</li>
   <li> you're done! No other upgrade procedure is required</li>
 </ul>
+    <em>Important:</em> If you are updating to 1.11.16 on a system that was initially installed before 2016 (before version 1.11.0),
+    you will need to download <a href="https://raw.githubusercontent.com/chamilo/chamilo-lms/5e0fc76649a7377c12cd0220ad1c0eae3f5eeaeb/tests/scripts/fix_quiz_id_to_iid.php">this file</a>,
+    drop it in your main/inc/ directory, edit it, remove the <pre>exit;</pre> on line 15, then load it in your browser
+    as https://yoursite.com/main/inc/fix_quiz_id_to_iid.php. This will fix an issue with inconsistent quiz, quiz
+    questions and answers internal numbering that existed prior to year 2016 (version 1.11.0). If your system was initially
+    installed with version 1.11.0 or superior, you don't need to do anything.
+
 <h3>3.2 Upgrading from Chamilo 1.10.x</h3>
 <ul>
   <li> check that you haven't left any customised stylesheet or image <span class="text-muted">(if you have, make sure you keep a copy on the side*)</span></li>