Update README.rst

Some parts where outdated, let's write this differently. Also, fix
spelling of OpenStack.

Change-Id: I97344264cd31e493644e8ab15f6c2a45fcb10dc6
sentence was unclear, moved the word "on"
changed subject and predicate for clarity

Change-Id: I45c4b654f6f64ae48a329e92720c95c117c84747
Merge "sentence was unclear, moved the word "on" changed subject and predicate for clarity"
Merge "Update README.rst"