Improve doc content

[adamltyson]

Linked to #36, but more about the content itself rather than the presentation:

Going through the docs as a user, I think there's room for improvement:

• Separate information about the cookiecutter from the commands needed to be typed
• Clarify how users can create a GitHub repo #57
• Include commands for both ssh & https usage (my feeling is that most non-developers use https)
• Add some kind of branching. e.g. we have the commands for modern git and git <v2.28 next to each other, I don't think this is as clear as it can be
• I think the push command should be git push --set-upstream origin main. The remote won't have any branches