If you reach the point where you releasing something based on our codebase you have a GPL obligation to provide sources for your changes, and the easiest way to fulfil the obligation is pushing changes to an online repo, ideally github. If you want people to review work you need to make your work review-able. The easiest way of doing that is pushing changes to an online repo, ideally github. Spot the theme?
Git can be tricky at first, but everyone started out as a novice user and everyone remembers that. If you need help to make the leap, ask.