readme text around tests might be stale

[matthewluckie]

The readme says

Tests are in the tests/ directory and can be run with python setup.py nosetests.

However, there's no nosetests:

usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
or: setup.py --help [cmd1 cmd2 ...]
or: setup.py --help-commands
or: setup.py cmd --help
error: invalid command 'nosetests'

Looking in

https://github.com/mjschultz/py-radix/blob/main/.github/workflows/python-package.yml#L57

perhaps the tests documentation should be

Tests are in the tests/ directory and can be run with pytest -v

but I'm not 100% sure on that.