Retarget CI to main and update README to use main branch

[aaronchongth]

Update CI and documentation

• Re-target CI to use main branch
• Documentation to point to main as well

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.57%. Comparing base (d7c082c) to head (da73520).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #165   +/-   ##
=======================================
  Coverage   63.57%   63.57%           
=======================================
  Files           8        8           
  Lines         799      799           
  Branches       97       97           
=======================================
  Hits          508      508           
  Misses        274      274           
  Partials       17       17           

Flag	Coverage Δ
tests	63.57% <ø> (ø)

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