Adjusted README to PostgreSQL version 13

\approve @ds

README.rst

@@ -2,18 +2,17 @@
 Docker OBM Database
 ===================
 
-This is a Docker container for the 
-`OpenBuildingMap <https://openbuildingmap.org>`__ database. It is based
-on PostgreSQL 12 with PostGIS 2.5 and is ready to be fed with
+This is a Docker container for the `OpenBuildingMap <https://openbuildingmap.org>`__
+database. It is based on PostgreSQL 13 with PostGIS 3 and is ready to be fed with
 OpenStreetMap data with osm2pgsql.
 
-It extends the official `Docker Library Postgres Container <https://github.com/docker-library/postgres/tree/master/12>`__
+It extends the official `Docker Library Postgres Container <https://github.com/docker-library/postgres/tree/master/13>`__
 with PostGIS.
 
 Copyright and copyleft
 ----------------------
 
-Copyright (c) 2020
+Copyright (C) 2020-2021
 
 * Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum GFZ