Add sample graphic to pypi page

[Travis Bear]

Update the README to link back to an image hosted on readthedocs. Here's how the colorama guys did it:

.. image:: http://colorama.googlecode.com/hg/screenshots/ubuntu-demo.png :width: 661 :height: 357 :alt: ANSI sequences on Ubuntu under gnome-terminal.

See http://code.google.com/p/colorama/source/browse/README.txt