[Docs] Chinese Document of faq

[wHao-Wu]

• Add Chinese Document of faq
• Refine a typo in faq

[codecov]

Codecov Report

Merging #730 (615cb1e) into master (2f95eb7) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #730      +/-   ##
==========================================
+ Coverage   48.91%   48.96%   +0.04%     
==========================================
  Files         208      208              
  Lines       15866    15880      +14     
  Branches     2546     2538       -8     
==========================================
+ Hits         7761     7775      +14     
+ Misses       7609     7603       -6     
- Partials      496      502       +6     

Flag	Coverage Δ
unittests	48.96% <ø> (+0.04%)	⬆️

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

Impacted Files	Coverage Δ
mmdet3d/models/detectors/single_stage.py	58.62% <0.00%> (-17.57%)	⬇️
mmdet3d/datasets/scannet_dataset.py	78.51% <0.00%> (-9.34%)	⬇️
mmdet3d/models/detectors/imvotenet.py	26.66% <0.00%> (ø)
mmdet3d/models/dense_heads/fcos_mono3d_head.py	12.10% <0.00%> (+0.13%)	⬆️
...et3d/models/dense_heads/anchor_free_mono3d_head.py	65.31% <0.00%> (+6.67%)	⬆️

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[wHao-Wu]

@xiliu8006
I'm not sure whether the Chinese meaning is suitable for explaining the problem in the English document.

[xiliu8006]

I think we can change the '使得在调用 np.dtype 会产生子类' to "more details on this issue"， Change it on English version please

[wHao-Wu]

@Tai-Wang
Comments resolved.