Use different editor?

Instead of nano, how about we use a system-default editor (NotePad or TextEdit, see c94736e2 & https://github.com/progit/progit2/pull/1331)? Learners can then point & click to save & close, instead of having to use new keyboard shortcuts (in addition to the git commands).

My experience is that both nano & vi(m) impose cognitivie load that is not necessary for this lesson. So, switching to nano makes no more or less sense than using vi(m), but since we teach git config core.editor anyway, we might as well use that to switch to a basic GUI editor or let learners set the one they already use.