proposal: script for mapping git branch to code folder

[skyzh]

For example, when I was composing the tutorial for the storage world, I'd want to...

• Create a base branch for world-3
• Adding commits
• Sometimes, revisit previous commits to make modifications (and apply them to all future commits)

It is hard to "revisit previous commits" with the current codebase structure. Therefore, I would like to try the git-branch-based workflow in the storage world, and use a script to copy the content on each branch to the final tutorial repo.