Adapt Readme and getting started to point out the supported versions

Author: uvchik

README.rst

@@ -24,14 +24,14 @@ Go to the `download page <http://readthedocs.org/projects/windpowerlib/downloads
 Installation
 ============
 
-If you have a working Python3 environment, use pypi to install the latest windpowerlib version. We highly recommend to use virtual environments.
+If you have a working Python 3 environment, use pypi to install the latest windpowerlib version. We highly recommend to use virtual environments.
 
 ::
 
     pip install windpowerlib
 
-So far, the windpowerlib is tested on python > 3.5 but seems to work down to 2.7.
-Please see the `installation page <http://oemof.readthedocs.io/en/stable/installation_and_setup.html>`_ of the oemof documentation for complete instructions on how to install python on your operating system.
+The windpowerlib is designed for Python 3 and tested on Python >= 3.5.
+Please see the `installation page <http://oemof.readthedocs.io/en/stable/installation_and_setup.html>`_ of the oemof documentation for complete instructions on how to install python and a virtual environment on your operating system.
 
 Optional Packages
 ~~~~~~~~~~~~~~~~~

doc/getting_started.rst

@@ -23,14 +23,14 @@ Go to the `download page <http://readthedocs.org/projects/windpowerlib/downloads
 Installation
 ============
 
-If you have a working Python3 environment, use pypi to install the latest windpowerlib version. We highly recommend to use virtual environments.
+If you have a working Python 3 environment, use pypi to install the latest windpowerlib version. We highly recommend to use virtual environments.
 
 ::
 
     pip install windpowerlib
 
-So far, the windpowerlib is tested on python > 3.5 but seems to work down to 2.7.
-Please see the `installation page <http://oemof.readthedocs.io/en/stable/installation_and_setup.html>`_ of the oemof documentation for complete instructions on how to install python on your operating system.
+The windpowerlib is designed for Python 3 and tested on Python >= 3.5.
+Please see the `installation page <http://oemof.readthedocs.io/en/stable/installation_and_setup.html>`_ of the oemof documentation for complete instructions on how to install python and a virtual environment on your operating system.
 
 Optional Packages
 ~~~~~~~~~~~~~~~~~