add LICENSE file

LICENSE

+Copyright © 2013 Felix Yan <felixonmars@archlinux.org>
+This work is free. You can redistribute it and/or modify it under the
+terms of the Do What The Fuck You Want To Public License, Version 2,
+as published by Sam Hocevar. See below for more details.
+
+            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
+                    Version 2, December 2004
+
+ Copyright (C) 2004 Sam Hocevar <sam@hocevar.net>
+
+ Everyone is permitted to copy and distribute verbatim or modified
+ copies of this license document, and changing it is allowed as long
+ as the name is changed.
+
+            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. You just DO WHAT THE FUCK YOU WANT TO.