Add documentation

[iacopy]

Best practices: Structuring Your Project

Testing:

• https://plainenglish.io/blog/unit-testing-in-python-structure-57acd51da923
• https://docs.python-guide.org/writing/tests/
• https://realpython.com/python-testing/

Patching, mocking

• https://levelup.gitconnected.com/unit-testing-in-python-mocking-patching-and-dependency-injection-301280db2fed