Readme should include how to install sphinx-rtd-theme

[iandobbie]

If you try to build the docs locally with sphinx as suggested in the README you need to install the sphinx-rtd-theme as well as sphinx. This should probably be added to the readme.

eg

 It can be built locally with::
 
    $ pip install sphinx
    $ pip install sphinx-rtd-theme
    $ sphinx-build -b html docs/source/ docs/build/html