Docs: Have a section for issues users coming from coverage may experience, surface it on or near the front page.

[stuaxo]

The readme mentions [1] that sys.path doesn't include CWD, but it would be good to have a specific section for users coming from coverage.

I have to admit to skimming over that bit when trying to work out why my test coverage went from 91% to 31%. It would be good to have a section, or link to a section - on the front page for issues users may experience coming from coverage.

https://pytest-cov.readthedocs.io/en/latest/readme.html?highlight=sys.path#overview