Working Locally: add link to info on solving locally

https://exercism.org/docs/using/solving-exercises/working-locally

In the Solving the Exercise section: add a link to https://code.visualstudio.com/docs/python/testing that explains how to set up testing using the provided *_test.py files.

I found this link to be very useful with setting up the provided tests and think others may too.
It would be good info to put on this page because it is expands upon the info already provided on the test files.