Update whatsnew.

whatsnew.htm

@@ -30,6 +30,7 @@ For conditions of distribution and use, see <a href="https://jrsoftware.org/file
 
 <p><a name="6.2.3"></a><span class="ver">6.2.3-dev </span><span class="date">(?)</span></p>
 <ul>
+  <li>Added support for IIS group users identifiers (<tt>iisiusrs</tt>) for use in <tt>Permissions</tt> parameters, contributed by Achim Stuy.</li> 
   <li>Added official Korean translation.</li>
 </ul>