wx: Add licence header file to wxMain.cpp

Please double check it's correct :)

desmume/src/wx/wxMain.cpp

@@ -1,3 +1,23 @@
+/* main.cpp - this file is part of DeSmuME
+ *
+ * Copyright (C) 2003-2009 Dolphin Project
+ * Copyright (C) 2009-2011 DeSmuME Team
+ *
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This file is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
 
 #include "wxMain.h"
 #include "NDSSystem.h"