added todo

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

de.srsoftware.oidc.web/src/main/resources/en/todo.html

@@ -13,6 +13,7 @@
         <div id="content">
             <h1>to do…</h1>
             <ul>
+              <li>implement brute-force countermeasures</li>
 	      <li>implement token refresh</li>
               <li>Configuration im Frontend</li>
             </ul>