Add GPL License header

usbrelay.c

@@ -1,5 +1,21 @@
-/* control usb relay hid devices*/
-/* ./relay SERIAL/relay_no/state SERIAL/relay_no/state ... */
+/*
+usbrelay: Control USB HID connected electrical relay modules
+Copyright (C) 2014  Darryl Bond
+
+This program 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 of the License, or
+(at your option) any later version.
+
+This program 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; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
 #include <stdio.h>
 #include <wchar.h>
 #include <string.h>