setup.py: set long_description by reading in the README
'qrcode' needs 'six' but its setup.py does not install it

KeySync might use 'six' in the future as well. Also, I fixed the alphasort
on the dependencies list.
setup.py: if using Python < 2.7, then include 'argparse' as dep

argparse was added to the standard Python libraries in Python 2.7, so if
KeySync is running on an older version of Python, then be sure that
argparse is installed.
document dependencies in README and setup.py