Add license header

gui/index.html

@@ -1,4 +1,9 @@
 <!DOCTYPE html>
+<!--
+Copyright (C) 2014 Jakob Borg and other contributors. All rights reserved.
+Use of this source code is governed by an MIT-style license that can be
+found in the LICENSE file.
+-->
 <html lang="en" ng-app="syncthing" ng-controller="SyncthingCtrl" class="ng-cloak">
 <head>
   <meta charset="utf-8">