Created by: wojtuss

This patch updates the document on QAT INT8 MKL-DNN transformation. It is related to the issue https://github.com/PaddlePaddle/Paddle/issues/23034 and PRs https://github.com/PaddlePaddle/Paddle/pull/23104 and https://github.com/PaddlePaddle/Paddle/pull/23284.

test=develop test=document_fix