Update doc

Author: jcs090218

README.md

@@ -16,3 +16,21 @@
 
 - [WzLib](https://github.com/hadeutscher/MapleLib) by @hadeutscher
 - [NAudio-Unity](https://github.com/WulfMarius/NAudio-Unity) by @WulfMarius
+
+## License
+
+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 3 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, see https://www.gnu.org/licenses/.
+
+See
+[COPYING](https://github.com/MapleStoryUnity/UnityWzLib/blob/master/COPYING)
+for details.