Switch to a restructuredtext README file

To make the README file showup in a more readable manner
on pypi and on other external sites convert the README from
the markdown format and move it to the restructuredtext format
which displays better on those external sites (and keeps our
documentation consistently one format).

Change-Id: I38f7152c264bbc0ebcf4a539b36f8b21e86705b8
Merge "Switch to a restructuredtext README file"