[Doc] Add semantickitti md

[sunjiahao1999]

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Motivation

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Modification

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BC-breaking (Optional)

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Checklist

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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

Patch and project coverage have no change.

Comparison is base (35fd839) 47.01% compared to head (bbc1513) 47.01%.

❗ Current head bbc1513 differs from pull request most recent head 8a7f4f0. Consider uploading reports for the commit 8a7f4f0 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           dev-1.x    #2515   +/-   ##
========================================
  Coverage    47.01%   47.01%           
========================================
  Files          276      276           
  Lines        23105    23105           
  Branches      3602     3602           
========================================
  Hits         10862    10862           
  Misses       11557    11557           
  Partials       686      686           

Flag	Coverage Δ
unittests	47.01% <ø> (ø)

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[JingweiZhang12]

Please update docs docs/en/user_guides/dataset_prepare.md