Add license notice to README

README.md

@@ -13,3 +13,13 @@ The "board" view is useful as an overview: https://gitlab.com/tildes/tildes/boar
 ## Contributing to Tildes development
 
 Please see [the Contributing doc](CONTRIBUTING.md) for more detailed information about setting up a development version of Tildes and how to contribute to development.
+
+## License
+
+Copyright (C) 2018 Tildes
+
+This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero 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 Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.