[css-lists-3] Update Changes section

Author: xfq

css-lists-3/Overview.bs

@@ -1435,8 +1435,15 @@ Acknowledgments</h2>
 	Simon Montagu (Mozilla, smontagu@smontagu.org)
 
 
-<h2 class="no-num" id="changes">
-Changes From CSS2.1</h2>
+<h2 class="no-num" id="changes">Changes</h2>
+
+This section documents the changes since previous publications.
+
+<h3 id="changes-20140320">Changes since the 20 March 2014 WD</h3>
+
+Use <<custom-ident>> consistently for counter names.
+
+<h3>Changes From CSS2.1</h3>
 
 	<p>As described in the introduction section, there are significant changes in this module when
 	compared to CSS2.1.