Add setup.py stub to support editable installs

[ktbarrett]

How would this feature be useful?
Editable installs are very useful for development, but without the presence of a setup.py file pip refuses to install the project in editable mode.

Describe the solution you'd like
A simple stub for setup.py is sufficient to support editable installs since setup.cfg is used for all project description. See below for an example of what that sub would look like.

from setuptools import setup


setup()

Describe alternatives you've considered
Manually installing nox after every change...

[FollowTheProcess]

You don't need a setup.py shim to do editable installs anymore!

Mine works as is:

If yours does not allow this you need to upgrade a newer version of pip and/or setuptools

We removed setup.py here: #458 (comment)