Added readme

README.md

+# pycdstar3: Library and command-line client for GWDG CDSTAR 3.x
+
+This is a client library and command-line toolbelt for accessing a
+[GWDG CDSTAR 3.x](https://cdstar.gwdg.de/) repository, written in Python (3.4+)
+and designed to be extensible and used for building your own tools and workflows.
+
+There is already a library called [pycdstar](https://pypi.org/project/pycdstar/)
+for accessing older versions of CDSTAR. The two libraries may be merged at some
+point, but for now, use [pycdstar](https://pypi.org/project/pycdstar/) for
+CDSTAR 2 and [pycdstar3](https://gitlab.gwdg.de/cdstar/pycdstar3) for CDSTAR 3
+and newer.
+
+
+
+## License
+
+    Copyright 2019 Marcel Hellkamp
+    
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+    
+        http://www.apache.org/licenses/LICENSE-2.0
+    
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+