docs: add contributing guidelines

[gurpreetatwal]

Asana: https://app.asana.com/0/1122465745219696/1205286509029023/f

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.41%. Comparing base (fcdea09) to head (8f27ec7).
Report is 17 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #141      +/-   ##
============================================
+ Coverage     68.74%   71.41%   +2.67%     
- Complexity      235      293      +58     
============================================
  Files            50       55       +5     
  Lines           995     1298     +303     
  Branches         69      101      +32     
============================================
+ Hits            684      927     +243     
- Misses          279      336      +57     
- Partials         32       35       +3     

Flag	Coverage Δ
integration	55.70% <ø> (+0.22%)	⬆️
test	51.30% <ø> (+5.17%)	⬆️

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see 9 files with indirect coverage changes

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[gurpreetatwal]

@wikiadrian 👀

[wikiadrian]

LGTM