PYPI metadata #93

[I'm hoping I'm posting this in the right project]

https://pypi.org/project/cryptojwt/ is missing some useful metadata: readme, homepage, etc.

Here's an example of working (I hope) setup.py: https://github.com/HENNGE/aapns/blob/c20e8c22805adb14facc3b00d34c15edf0613896/setup.py

For example, long_description also needs long_description_content_type.

And if you want to move to poetry please consider https://github.com/dimaqq/awaitwhat/blob/master/pyproject.toml (you don't need build because you don't have a C extension).