Added comment about fields types in changelog

documentation/changelog.html

@@ -55,7 +55,11 @@
 <h3>New Features</h3>
 <h3>Improvements</h3>
 <h3>Debugging</h3>
-
+<h3>Important changes</h3>
+<ul>
+  <li>Users and sessions extra fields of "double select" type have a modified syntax. If you used this field type in a previous version of Chamilo, you will probably need to update it manually from the database.</li>
+  <li></li>
+</ul>
 
 <h1>Chamilo 1.9.0 - Vogüé, 31st of July, 2012</h1>
 
@@ -2177,4 +2181,4 @@ a simple videoconferencing interface.</p>
         <img src="http://jigsaw.w3.org/css-validator/images/vcss-blue" style="margin: 1em; float: right;" alt="Valid CSS" />
     </a>
 </body>
-</html>
+</html>