Update API documentation links in README

[frederikprijck]

Changes

The API documentation link was missing in the README.

References

closes #1239

Testing

• This change adds unit test coverage
• This change adds integration test coverage

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.20%. Comparing base (f3c024f) to head (5c710cf).

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #1264    +/-   ##
========================================
  Coverage   78.20%   78.20%            
========================================
  Files         356      356            
  Lines       17746    17746            
  Branches     9555     9413   -142     
========================================
  Hits        13878    13878            
  Misses       3868     3868            

Flag	Coverage Δ
alltests	78.20% <ø> (ø)

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