Update README.md and CONTRIBUTING.md

[KKA11010]

• Added app store url
• Updated image
• Moved some content from readme to contributing

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 13.29%. Comparing base (faea4d6) to head (ea0a023).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #313   +/-   ##
=======================================
  Coverage   13.29%   13.29%           
=======================================
  Files         164      164           
  Lines        6153     6153           
  Branches     1687     1687           
=======================================
  Hits          818      818           
  Misses       5188     5188           
  Partials      147      147           

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