fixed documentation on README.rst

URL off documentation was already in the file, but was not being rendered correctly.

Remove crate.io references on README.rst and change to pypi.python.org.

crate.io domain was sold to bigdata company

http://www.reddit.com/r/Python/comments/1wcp93/what_happened_to_crateio/

crateio/crate.io#18

I think at the moment there is no substitute for crate.io.
Are developing a new pypi, which can be seen in [1]

[1] https://github.com/pypa/warehouse