Improve setup instructions

[wxtim]

Setup instructions

• Have student add rule to protect main
• Have them set up their own repo as part of the setup, (if it's completely new because they haven't done the prereq training they should tick box asking for README.md. Note after Git Push about following git's instructions on pushing a new branch - learners seemed to have forgotten this.) This will allow learners to be working entirely on their partner's repo until the review stage.