docs: update readme

[vonovak]

this makes the readme a little more digestable

• removes old useFcmV1 parameter
• removes immediately invoked function expressions from the readme, they make the code harder to read an anybody can figure out for themselves how they will structure their code

Test plan:

• TODO

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (50bf0e9) to head (f5a8712).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #146   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          168       168           
  Branches        33        32    -1     
=========================================
  Hits           168       168           

Flag	Coverage Δ
node_18	100.00% <ø> (ø)
node_20	100.00% <ø> (ø)
node_22	100.00% <ø> (ø)

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