documentation beef up (incl. example gallery and badge generation)

[pawelmagnu]

No description provided.

[slayoo]

Kudos @pawelmagnu
Among TODOs, we have:

• move tutorial snippets out of README into subsections of PySDM landing page
• make the moved snippets being executed on CI
• introduce badges into __init__.py for all examples
• populate examples table with keywords

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.60%. Comparing base (4c0f146) to head (075fd42).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1407   +/-   ##
=======================================
  Coverage   84.60%   84.60%           
=======================================
  Files         375      375           
  Lines        9248     9248           
=======================================
  Hits         7824     7824           
  Misses       1424     1424           

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