Introduction to Git needed

[oliverxchen]

@yc-ng noted that we should have a quick start for github

[oliverxchen]

should we point to external tutorials or have a tutorial that would be interesting to our volunteers?

[oliverxchen]

choose a GUI or just for command line?

[yc-ng]

I feel that we should first teach using the command line (like volunteer onboarding at datadive) - no need for screenshots which a GUI-based guide requires.

As for external tutorials, I think this might help: https://onlywei.github.io/explain-git-with-d3/