Upload sdist to PyPI

[abraha2d]

Would it be possible to build and upload the sdist to PyPI?

I'm looking to get thop onto conda-forge using grayskull, but that relies on an sdist being available for thop on PyPI (which is currently not the case).

As far as I can tell, this should be as simple as adding sdist to the GitHub Action here (so that it reads python setup.py sdist bdist_wheel), and the twine steps following it should take care of the rest.

[abraha2d]

I've submitted #204 to resolve this.