added banner for longhornphp conference

Author: DavertMik

_includes/hero.html

@@ -19,6 +19,7 @@ <h1>PHP Testing for <br>everyone<span class="blue">_</span></h1>
           Support</a>
       </div> <!-- /.row -->
       <div>
+        <a href="http://longhornphp.com" target="_blank"><img src="/images/longhornphp.jpg" alt="Longhorn PHP Conference"></a>
       </div>
     </div>
   </div>