Contrib docs

[rcolfin]

Adding CODE_OF_CONDUCT.md and CONTRIBUTING.md from https://contributing.md/generator/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.87%. Comparing base (3b7413a) to head (03da25c).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #74   +/-   ##
=======================================
  Coverage   66.87%   66.87%           
=======================================
  Files          10       10           
  Lines         951      951           
=======================================
  Hits          636      636           
  Misses        315      315           

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[GitBib]

Thanks for your contribution!