Git: Add token authentication set-up

[illicitonion]

Which module(s) and week(s) does this change effect?
Module(s): Git
Week(s): 3

What is the work that needs to be done?

GitHub are soon going to require auth tokens, instead of passwords: https://github.blog/2020-12-15-token-authentication-requirements-for-git-operations/

This won't affect Desktop, but as soon as the trainees are using the CLI we'll need to get them to do a one-time set-up.

Why is this work important to do?

GitHub access will otherwise break.

[ChrisOwen101]

This will probably want to be added as work in this lesson:
https://syllabus.codeyourfuture.io/git/cli/lesson

And/or as preparation work for the whole module
https://syllabus.codeyourfuture.io/git/preparation