[Doc] Add document on preparing datasets

[Ben-Louis]

Motivation

Modification

BC-breaking (Optional)

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (896e9d5) 82.25% compared to head (7e92a26) 82.26%.

❗ Current head 7e92a26 differs from pull request most recent head b0ac5b7. Consider uploading reports for the commit b0ac5b7 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##           dev-1.x    #2273    +/-   ##
=========================================
  Coverage    82.25%   82.26%            
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  Files          228      230     +2     
  Lines        13387    13552   +165     
  Branches      2268     2301    +33     
=========================================
+ Hits         11011    11148   +137     
- Misses        1862     1871     +9     
- Partials       514      533    +19     

Flag	Coverage Δ
unittests	82.26% <ø> (+<0.01%)	⬆️

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see 22 files with indirect coverage changes

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