`tutorial` command with tutorial aimed at first time users

[dbosk]

We'll add a tutorial written in markdown. The tutorial command can then render it in the terminal using the rich package (as done for submissions and assignments instructions).

The tutorial itself could potentially be divided across the chapters for the other commands. That way, each part of the tutorial comes closer to it's implementation and thus less risk of divergence over time.

[dbosk]

This is related to #56, but this is for non-developers.