Fix 2.4 section of docs page.

docs.phtml

@@ -239,6 +239,9 @@ include("externals/menu.phtml");
     </table>
   </li>
 </ul>
+<div class="downloadimage">
+<img alt="stabledoc" src="<?=$top_dir;?>/images/stabledoc.png" />
+</div>
 </div>
 
 <p class="justify"><?php echo T_("This is the old stable release of the <span class=\"gnucash\">GnuCash</span> documentation, corresponding to the 2.4.13 release of <span class=\"gnucash\">GnuCash</span> itself.");?></p>