Added license and very basic readme

README.rst

+========================
+openbuildingmap-data-api
+========================
+
+Copyright and copyleft
+----------------------
+
+Copyright (C) 2021
+
+* Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum GFZ
+
+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 http://www.gnu.org/licenses/.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If your software can interact with users remotely through a computer
+network, you should also make sure that it provides a way for users to
+get its source. For example, if your program is a web application, its
+interface could display a "Source" link that leads users to an archive
+of the code. There are many ways you could offer source, and different
+solutions will be better for different programs; see section 13 for the
+specific requirements.
+
+See the `LICENSE <./LICENSE>`__ for the full license text.