[Docs] Add useful_tools.md Chinese version

[ZCMax]

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Motivation

Add useful_tools.md Chinese version.

Modification

Add useful_tools.md Chinese version.

BC-breaking (Optional)

no

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Merging #728 (be8c531) into master (2f95eb7) will increase coverage by 0.02%.
The diff coverage is 40.98%.

❗ Current head be8c531 differs from pull request most recent head a577d95. Consider uploading reports for the commit a577d95 to get more accurate results

@@            Coverage Diff             @@
##           master     #728      +/-   ##
==========================================
+ Coverage   48.91%   48.94%   +0.02%     
==========================================
  Files         208      208              
  Lines       15866    15884      +18     
  Branches     2546     2538       -8     
==========================================
+ Hits         7761     7774      +13     
+ Misses       7609     7608       -1     
- Partials      496      502       +6     

Flag	Coverage Δ
unittests	48.94% <40.98%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...et3d/core/bbox/iou_calculators/iou3d_calculator.py	26.31% <ø> (ø)
mmdet3d/core/bbox/structures/base_box3d.py	75.00% <ø> (ø)
mmdet3d/core/bbox/structures/box_3d_mode.py	92.10% <ø> (ø)
mmdet3d/core/bbox/structures/cam_box3d.py	77.23% <ø> (ø)
mmdet3d/core/bbox/structures/depth_box3d.py	84.09% <ø> (ø)
mmdet3d/core/bbox/structures/lidar_box3d.py	84.21% <ø> (ø)
mmdet3d/datasets/kitti_mono_dataset.py	63.98% <ø> (-0.16%)	⬇️
mmdet3d/datasets/lyft_dataset.py	71.35% <ø> (ø)
mmdet3d/datasets/nuscenes_mono_dataset.py	37.46% <0.00%> (-0.65%)	⬇️
mmdet3d/models/dense_heads/free_anchor3d_head.py	21.59% <ø> (ø)
... and 10 more

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[Wuziyi616]

主要是英文和中文之间的空格，以及 FLOPs 那段因为英文文档近日更新了所以需要修改一下

[Tai-Wang]

改完 comments 差不多可以 merge 了