Add instructions to documentation on how to run tests with pytest-bdd

[k2m30]

I am not the only one struggling with it. Here is Stackoverflow discussion started almost five years ago and still haven't solved.

[jzohrab]

I agree that a simple note in the readthedocs would help. The readme in this repo has an example.

Define your step definitions in a test_xxxx.py file, and your feature file somewhere, with a reference to that file in your step defs. Then when your run pytest, it will pick up the test and run it just like the others.