Add a branch for formatted sources

[vityaman]

Xv6 is poorly formatted and also we want to check our students code formatting before code review to make it more pleasant to read.

Problem is that we can not format actual sources as it will be incompatible changes with the original repository and so we will get a lot of merge conflicts.

But what we can really do is to make a separate branch with formatted sources. The branch will be different from main in an only thing - is that sources clang-format will be formatted. This branch will be updated using force push.

Plan

• Add a branch named format from main.
• Add clang-format config to format branch. Can be stolen from algocont.
• Format sources using clang-format at format.
• Update format branch.

[vityaman]

We decided that students must suffer.