Docs request: example setup.cfg

[jamesbraza]

From #69 it looks like config files are supported.

Can you document how to add a setup.cfg entry for flake8-eradicate in the README.md? Specifically how to whitelist with eradicate-whitelist-extend.

--eradicate-whitelist-extend to extend the whitelist from eradicate (# separated list)

Also, what is a # separated list?

---

For example, I need to whitelist this line:

# Formula: (counts/distance) = (counts/step) (steps/turns) (turns/distance)

[SudoCerb]

+1

This is not immediately clear