[Feature] Avoid dupliate placeholder docs in CN

[gaotongxiao]

Motivation

In the past, to maintain the structure of Chinese docs, we have to manually sync markdowns with EN docs. It's troublesome and introduces many duplicated markdowns in practice.

Modifications

1. Add cp_origin_docs.sh to docs_zh_CN which copies all non-translated *.md files from EN docs to CN docs when building CN docs.
2. Remove duplicated placeholder docs in CN directory.

[codecov]

Codecov Report

Merging #582 (57bb529) into main (c39f116) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #582   +/-   ##
=======================================
  Coverage   84.95%   84.95%           
=======================================
  Files         143      143           
  Lines        9796     9796           
  Branches     1414     1414           
=======================================
  Hits         8322     8322           
  Misses       1147     1147           
  Partials      327      327           

Flag	Coverage Δ
unittests	84.95% <ø> (ø)

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Impacted Files	Coverage Δ
mmocr/models/textrecog/convertors/seg.py	91.78% <0.00%> (ø)

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