chore(test): add description for the examples directory

[imjuni]

• Added README.md file explaining the examples directory
• Added testcase: improve test coverage

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (82e6649) to head (f19c0c8).

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #136      +/-   ##
===========================================
+ Coverage   99.95%   100.00%   +0.04%     
===========================================
  Files          75        77       +2     
  Lines        2472      2491      +19     
  Branches      370       372       +2     
===========================================
+ Hits         2471      2491      +20     
+ Misses          1         0       -1     

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