add esp32 build document and ci Refs #5536

[luxincn]

add esp32 build doc and ci Refs #5536

[tencent-adm]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.86%. Comparing base (4c3deba) to head (534d665).
Report is 14 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #5567       +/-   ##
===========================================
- Coverage   94.66%   89.86%    -4.80%     
===========================================
  Files         787      264      -523     
  Lines      248712    77232   -171480     
===========================================
- Hits       235432    69403   -166029     
+ Misses      13280     7829     -5451     

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[nihui]

Thanks for your contribution !