Modify compatibility note

lavagetto · lavagetto · commit c37e8beea599 · 2015-05-19T17:48:21.000+02:00
Since we're breaking backwards compatibility (sort of) let's declare
we're going to support 2.0.x or newer from now on.
diff --git a/README.rst b/README.rst
@@ -14,7 +14,7 @@ Installation
 Pre-requirements
 ~~~~~~~~~~~~~~~~
 
-Install etcd (0.2.rc1 or later). This version of python-etcd will only work correctly with the etcd API version 2.
+Install etcd (2.0.1 or later). This version of python-etcd will only work correctly with the etcd version 2.0.x or later. If you are running an older version of etcd, please use python-etcd 0.3.3 or earlier.
 
 This client is known to work with python 2.7 and with python 3.3 or above. It is not tested or expected to work in more outdated versions of python.
 
