Add license.

COPYING.txt

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+Xonotic Statistics Application (XonStat): an application to handle the 
+parsing, storage, and presentation of statistical data produced by the 
+open source first person shooter game Xonotic. 
+
+Copyright (C) 2010-2011 Ant Zucaro
+
+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
+
+You can contact Ant Zucaro at azucaro at gmail dot com.