Add instructions to README.md

Signed-off-by: Timur Tabi <timur@tabi.org>
Add make_mini.py program

Add the main make_mini.py program.  It supports reading images from files
or the Internet.  It can extract a label from the image using the exiv2
tool.  It requires ImageMagick and the Wand Python package
(http://wand-py.org).  The easiest way to install exiv2 and ImageMagick
is via the MacPorts project (http://www.macports.org/).

Signed-off-by: Timur Tabi <timur@tabi.org>