Add license file to the repository root

LICENSE.rst

+Documentation
+-------------
+
+Copyright (C) 2018-2019 Provincia Autonoma di Bolzano
+
+This work is licensed under the Creative Commons Attribution-ShareAlike
+4.0 International License. To view a copy of this license, visit
+http://creativecommons.org/licenses/by-sa/4.0/ or send a letter to
+Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
+
+Code snippets
+-------------
+Copyright (C) 2018-2019 Provincia Autonoma di Bolzano
+
+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 <http://www.gnu.org/licenses/>.

README.rst

@@ -25,7 +25,3 @@ Licenze
 .. image:: https://img.shields.io/badge/documentation-CC%20BY--SA-lightgrey.svg
     :target: https://creativecommons.org/licenses/by-sa/4.0/
     :alt: Documentation CC BY-SA
-
-.. image:: https://img.shields.io/badge/screenshots-CC0-ff69b4.svg
-    :target: https://creativecommons.org/publicdomain/zero/1.0/
-    :alt: Screenshots CC0