[llvm] [DebugInfo][RemoveDIs] Add documentation for updating code to handle debug records (PR #93562)

[J. Ryan Stinnett via llvm-commits]

jryans wrote:

What's the status of https://github.com/llvm/llvm-project/pull/91725? That seems to update some of the same text (at least the summary paragraph at the top). Maybe it was forgotten? Perhaps best to merge that first and then rebase this to avoid conflicts.

https://github.com/llvm/llvm-project/pull/93562