Master branch should be protected

[ajdubovoy]

Context: 8e0e5fa

It looks like someone accidentally committed to master, which created temporary weird effects for students on setup day 🙀

Since this is a...fairly important repo, can we please lock the master branch? I'd do it myself but I don't have permissions. Maybe @Eschults, you have to do it?

Thanks so much!

[Eschults]

👋 I added branch rules this morning, also the repo has limited Write accesses since the beginning, so not sure what happened here 🤔

Branch protection rules should prevent this from happening in the future 👌

[ajdubovoy]

Thank you!!