also updated README

Fixes #16

Thank you!

"Diceware 8192 list" is not a valid reference any more.

This wordlist was renamed to `en`. It is the default wordlist.

Remove heading of configuration file section of README. It was more confusing than helpful, I think.

If we talk about configuration _files_, then tell it.

Give hints, how to customize configuration.

Tell about dash by name.

The README is evaluated by standard docutils when released on
pypi.python.org. These do not understand most text roles (like
``:class:``) recognized by `Sphinx`. As a result the README will be
displayed as raw text on PyPI which looks ugly.