[Doc] Add Chinese version of 1_exist_data_model doc

[AronLin]

Add Chinese version of 1_exist_data_model doc

[codecov]

Codecov Report

Merging #5423 (0fdab5d) into master (595b517) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 0fdab5d differs from pull request most recent head 58a06ed. Consider uploading reports for the commit 58a06ed to get more accurate results

@@            Coverage Diff             @@
##           master    #5423      +/-   ##
==========================================
- Coverage   65.25%   65.25%   -0.01%     
==========================================
  Files         276      276              
  Lines       21531    21528       -3     
  Branches     3563     3560       -3     
==========================================
- Hits        14051    14048       -3     
+ Misses       6727     6726       -1     
- Partials      753      754       +1     

Flag	Coverage Δ
unittests	65.23% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
mmdet/models/dense_heads/anchor_head.py	86.72% <ø> (ø)
mmdet/models/dense_heads/autoassign_head.py	96.11% <100.00%> (-0.07%)	⬇️
mmdet/models/utils/normed_predictor.py	83.33% <0.00%> (-9.53%)	⬇️
mmdet/models/roi_heads/test_mixins.py	55.64% <0.00%> (-1.62%)	⬇️
mmdet/models/roi_heads/mask_heads/fcn_mask_head.py	73.25% <0.00%> (+3.48%)	⬆️

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[ZwwWayne]

LGTM and can be merged after resolving comments, @hhaAndroid may check again before approval