[llvm] [LFI][Doc] Update documentation for planned features (PR #192128)

[Zachary Yedidia via llvm-commits]

zyedidia wrote:

Thanks for the suggestions, I've updated the doc. Is the consensus to keep the file as `LFI.rst`? If not, please let me know, otherwise I'll merge this shortly.

https://github.com/llvm/llvm-project/pull/192128