Merge pull request #86 from firedrakeproject/rckirby/addlicense

add license file

LICENSE

@@ -0,0 +1,13 @@
+Irksome is free software: you can redistribute it and/or modify it under
+the terms of the GNU Lesser General Public License as published by the
+Free Software Foundation, either version 3 of the License, or (at your
+option) any later version.
+
+Irksome 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with Irksome. If not, see <http://www.gnu.org/licenses/>.
+