Fix pypi push by specifying a long_description

[achantavy]

Pypi publish has been breaking since 0.67.0: https://github.com/lyft/cartography/actions/runs/3716067385/jobs/6301965332.

The error message was

ERROR    `long_description` has syntax errors in markup and would not be rendered on PyPI.
         No content rendered from RST source.

Repro

I searched and found a hint in pypa/twine#454. I was able to reproduce the error locally by installing twine (at 4.0.2) with pip install twine, building a dist with python -m pip install build && python -m build --sdist --wheel --outdir dist/ ., and then running twine check dist/*.

Fix

I added a long_description field to setup.py and re-ran twine and it passed:

I'm not sure if long_description is now mandatory, but at this point I just want my release to stop breaking and to be published to pypi.

I've also filed pypa/twine#960.