Add pypi badge (#25)

Author: LKaemmerling

README.rst

@@ -6,7 +6,8 @@ Hetzner Cloud Python
     :target: https://travis-ci.com/hetznercloud/hcloud-python
 .. image:: https://readthedocs.org/projects/hcloud-python/badge/?version=latest
     :target: https://hcloud-python.readthedocs.io
-
+.. image:: https://img.shields.io/pypi/pyversions/hcloud.svg
+    :target: https://pypi.org/project/hcloud/
 
 
 **IMPORTANT: This project is still in development and not ready production yet!**
@@ -57,4 +58,4 @@ License
 -------------
 The MIT License (MIT). Please see `License File`_ for more information.
 
-.. _License File: https://github.com/hetznercloud/hcloud-python/blob/master/LICENSE
+.. _License File: https://github.com/hetznercloud/hcloud-python/blob/master/LICENSE