Rewrite README and include as "about" in docs

Didn't fix this one because it is [valid](http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#sections):

> An underline/overline is a single repeated punctuation character that begins in column 1 and forms a line extending at ***least as far*** as the right edge of the title text.

And looks nicer, don't you think?

And also conforms with Python's docs.