Improve README.md and docu

[ufechner7]

• fix link
• add page Development
• add diagram

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.59%. Comparing base (7f35215) to head (4c2a16e).
⚠️ Report is 45 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #48   +/-   ##
=======================================
  Coverage   61.59%   61.59%           
=======================================
  Files          15       15           
  Lines         677      677           
=======================================
  Hits          417      417           
  Misses        260      260           

Flag	Coverage Δ
unittests	61.59% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ufechner7]

@davidanthoff Please, review!