Update readme and docs

[szabo137]

This updates the readme and docs adopting the current iteration on the implementation of the interface.

Related issues

Closes #25

Checklist

• write the tutorials for four-vectors
• write the tutorials for coordinate systems
• rewrite the description of the interface (clarification and opting out parts to the other doc sections)
• Tests are passing
• Docs were updated and workflow is passing

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.33%. Comparing base (cf892a6) to head (8c2cfa6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
+ Coverage   93.91%   94.33%   +0.42%     
==========================================
  Files           4        5       +1     
  Lines         148      159      +11     
==========================================
+ Hits          139      150      +11     
  Misses          9        9              

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