Add note on supported Python versions to readme.
Welcome to Apache Libcloud's documentation!
===========================================
+.. note::
+
+ Libcloud v3.0.0 dropped support for Python 2.7 and Python 3.4 and now only
+ supports Python version >= 3.5.
+
+ If you still need to us Libcloud with one of the new unsupported versions,
+ you can do that by using the latest release of Libcloud which still supports
+ those versions (Libcloud v2.8).
+
Apache Libcloud is a Python library which hides differences between different
cloud provider APIs and allows you to manage different cloud resources through
a unified and easy to use API.
