docs: add copy of examples to lib.md

[kazuk]

Issue number and link

Fixes: #105

Describe your changes

add document code copy from examples.

Checklist before requesting a review

• I follow the Semantic Pull Requests rules (bugfix/feature)
• I specified links to related issues (must: bugfix, want: feature)
• I have performed a self-review of my code (bugfix/feature)
• I have added thorough tests (bugfix/feature)
• I have edited ## [Unreleased] section in CHANGELOG.md following keep a changelog syntax (bugfix/feature)
• I {made/will make} a related pull request for documentation repo (feature)

[codecov]

Codecov Report

Merging #156 (5a24bd2) into main (8b2cbf8) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #156      +/-   ##
==========================================
+ Coverage   87.79%   87.82%   +0.02%     
==========================================
  Files         203      203              
  Lines       12620    12620              
==========================================
+ Hits        11080    11083       +3     
+ Misses       1540     1537       -3     

Impacted Files	Coverage Δ
..._engine/autonomous_executor/row/value/sql_value.rs	75.51% <0.00%> (+0.68%)	⬆️
springql-core/src/expression.rs	75.44% <0.00%> (+1.19%)	⬆️

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[laysakura]

🙌