New function add_chart

[wanghaochen2024]

• Update unit tests and docs for the function
• Simplify example code in README

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (aeb5cfc) to head (1dc9056).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main        #2    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files            4         4            
  Lines          513       696   +183     
==========================================
+ Hits           513       696   +183     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[xuri]

LGTM, thanks for your contribution.