ITP - Onboarding Sprint 3 - New Git material

There are two more Git topics to cover:

- Undoing a Commit
- Ignoring files

We can build on the repo used in previous sprints here and look at the differences between `git reset` and `git revert`. Creating a `.gitignore` file may be a bit too much here, especially since there's not really any need for one, but we should cover it somewhere before we're dealing with things like environment variables later in the course.