adding authors.rst, contributing.rst and readme.rst to docs.

Also changed 'CONTRIBUTORS.txt' to 'AUTHORS.txt' following the example of https://github.com/audreyr/cookiecutter-pypackage
and also django (they use only 'AUTHORS' there, but I the idea is the same).
Add link to virtualenv and virtualenvwrapper docs can be good for beginners in python world.
In my current job, I'm the one that uses python, all others use Java.
Good documentation makes things less complicated.