docs: improve global structure

[lars-reimann]

Closes #1029

Summary of Changes

• Separate explanation of the pipeline and the stub language.
• Explain segments after comments. They are not needed to get started.
• Improve home page.
• Improve installation guide.
• Improve home page of language reference.
• Improve documentation of packages.

[github-actions]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ CSS	stylelint	1	0	0	1.51s
✅ JAVASCRIPT	eslint	1	0	0	7.14s
✅ JAVASCRIPT	prettier	1	0	0	0.61s
✅ JSON	eslint-plugin-jsonc	2	0	0	1.4s
✅ JSON	jsonlint	2		0	0.28s
✅ JSON	npm-package-json-lint	yes		no	0.82s
✅ JSON	prettier	3	0	0	0.88s
✅ JSON	v8r	2		0	7.56s
❌ MARKDOWN	markdown-link-check	89		1	5.71s
✅ PYTHON	black	2	0	0	1.01s
✅ PYTHON	mypy	2		0	2.21s
✅ PYTHON	ruff	2	0	0	0.19s
✅ REPOSITORY	git_diff	yes		no	0.27s

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (8be49c5) to head (409b8e3).
Report is 122 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1023   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files           99        99           
  Lines        19051     19051           
  Branches      3902      3902           
=========================================
  Hits         19051     19051           

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[lars-reimann]

🎉 This PR is included in version 0.12.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• v0.12.0
• GitHub release

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