[css-writing-modes-3] Update Changes section

Author: kojiishi

css-writing-modes-3/Overview.bs

@@ -2466,6 +2466,7 @@ Privacy and Security Considerations {#priv-sec}
     <li>Deferred the ''sideways-lr'' and ''sideways-rl'' values of 'writing-mode' to Level 4.
     <li>Deferred the ''digits'' value of 'text-combine-upright' to Level 4.
     <li>Deferred the automatic multi-column behavior of orthogonal flows to Level 4.
+    <li>Added Privacy and Security Considerations section.
   </ul>
 
   <h3 class="no-num" id="changes-201311">