[llvm-debuginfo-analyzer] README

llvm-debuginfo-analyzer is a command line tool that processes debug
info contained in a binary file and produces a debug information
format agnostic “Logical View”, which is a high-level semantic
representation of the debug info, independent of the low-level
format.

https://discourse.llvm.org/t/llvm-dev-rfc-llvm-dva-debug-information-visual-analyzer/62570

This patch:

Contains notes collected during the development, review and test.
It describes limitations, know issues and future work.

Reviewed By: Orlando

Differential Revision: https://reviews.llvm.org/D144857