Problem: broken project description on pypi

Solution: replace README + CHANGELOG combi with description

Add a nice description in `setup.py` for `long description`.
Remove the README and CHANGELOG for the `long description`

[example for a nice description](https://pypi.org/project/BigchainDB/)

This should be done before the next release!

Start in setup.py and inspect how the current README and CHANGELOG are combined for the PyPI long description. Compare the rendered result with the linked BigchainDB example; done means setup.py uses the intended description and no longer uses the README/CHANGELOG combination before the next release.

Written by the indexing model from the issue text.