[llvm] [llvm][docs] Reorder sections in GitHub.rst (PR #134212)

[David Spickett via llvm-commits]

DavidSpickett wrote:

Yeah in some logical "walls of text don't scare me" way, branches and stacked pull requests are a decision you would make before you start, but 99% of the audience won't need it to begin with.

And it's not like uploading a branch from your fork to llvm/llvm-project, or converting a PR with many commits into a stacked PR is that hard to do.

I like the new order. Also a table of contents will mitigate order being a problem, surprised we didn't have one already.

https://github.com/llvm/llvm-project/pull/134212