add missing copyright header to Mod.cs

OpenRA.FileFormats/Mod.cs

@@ -1,4 +1,14 @@
-using System;
+#region Copyright & License Information
+/*
+ * Copyright 2007-2011 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made 
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;