clone, view changes side by side

[hwick]

add section about cloning
note how to look at changes from commits side by side

[hwick]

Cloning would be great for day 2 for people who didn't do the homework -- they can clone the pre-made learning-github repo

[hwick]

just adding a note here: day 2 went long and we didn't have time for class exercises at the end, but day 3 went by very quickly, so we could potentially re-allocate some material between days, or flesh out day 3 with some of the suggestions