Created by: NorthStar

Due to pre-commit issue, now I am using a new branch to replace https://github.com/PaddlePaddle/models/pull/304

Attempts to fix #4246 from Paddle: PaddlePaddle/Paddle#4246 , one round of review for English.

Note that the diagram says mAP for mean Value Precision, but when I look things up, they are all just MAP, so I corrected accordingly.