docs: complate README.md

[wolfogre]

close #6

[codecov]

Codecov Report

Merging #16 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #16   +/-   ##
=======================================
  Coverage   85.93%   85.93%           
=======================================
  Files           4        4           
  Lines         128      128           
=======================================
  Hits          110      110           
  Misses          9        9           
  Partials        9        9           

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