[css-pseudo] Add changes section

Author: fantasai

css-pseudo/Overview.bs

@@ -909,6 +909,18 @@ Addition to the <code>window</code> interface</h3>
   Its return value is a <code>CSSPseudoElementList</code>,
   potentially empty if no pseudo-element exists for the given element and the given type.
 
+<h2 class="no-num" id="changes">
+Changes</h2>
+
+  Changes since the <a href="https://www.w3.org/TR/2015/WD-css-pseudo-4-20150115/">15 January 2015 Working Draft</a> include:
+
+  <ul>
+    <li>Addition of the ''::marker'' pseudo-element.
+    <li>Defined handling of text decorations on ''::selection'' to match IE's more sensible behavior.
+    <li>Links to pseudo-element OM design discussions.
+    <li>Various minor clarifications.
+  </ul>
+
 <h2 class="no-num" id="acknowledgements">
 Acknowledgements</h2>