docs(README): add OSSF best pratices badge

[musicEnfanthen]

This PR adds another badge to the README

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.25%. Comparing base (b90d23d) to head (ffcdbff).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1463   +/-   ##
========================================
  Coverage    76.25%   76.25%           
========================================
  Files          244      244           
  Lines         3996     3996           
  Branches       608      608           
========================================
  Hits          3047     3047           
  Misses         929      929           
  Partials        20       20           

Flag	Coverage Δ
unittests	76.25% <ø> (ø)

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[masthom]

Soweit ich das beurteilen kann...