update doc

[yangwenmai]

No description provided.

[coveralls]

Coverage remained the same at 100.0% when pulling 3c124cf on develop into 693e23e on master.

[codecov]

Codecov Report

Merging #2 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master     #2   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines           2      2           
=====================================
  Hits            2      2

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[coveralls]

Coverage remained the same at 100.0% when pulling 8f30cba on develop into 693e23e on master.