missing dependencies for self-test

[tyrcho]

Hey, I'm a long time user of approval testing (on the JVM) but new on python.

I installed vscode / python and cloned this repo on a fresh machine.

When I follow the instructions from https://github.com/approvals/ApprovalTests.Python#pull-requests to run the self-tests I have several errors like ModuleNotFoundError: No module named 'numpy'

I resolved them by running

pip install empty_files
pip install typing_extensions
pip install mrjob
pip install numpy

Maybe something is missing from either the documentation or the list of dependencies installed by tox ?