Created by: linshuliang

I add two optional arguments --use_tb, --tb_log_dir in files tools/train.py && tools/infer.py, so users can choose whether to use tb-paddle to record data, so as to display in Tensorboard.

This new feature can bring greate convenience to view the parameters variation and original/bbox images.

Futhermore, I have modified the explanation in docs/GETTING_STARTED_cn.md.