[llvm] [llvm][Docs] Update MyFirstTypoFix doc (PR #79149)

[David Spickett via llvm-commits]

DavidSpickett wrote:

Inspired by https://github.com/llvm/llvm-project/pull/78292 where I'm consider whether to write some docs about what happens post merge, and the first step of that is to make sure what we have now is up to date.

@RalfJung feel free to review also if you wish to.

https://github.com/llvm/llvm-project/pull/79149