Documentation duplication

[2xB]

Currently there exist multiple public places of user documentation:

• On the "gh-pages" branch
• On the "main" branch in the Kassiopeia/Documentation folder
• In the main README

As far as I can tell, the Doxygen-based documentation is worse than browsing the source at the moment, so we can also get rid of it and potentially do it again from scratch in the future. We should however keep the logos somewhere. So I suggest removing:

• Documentation/{Reference,CMakeLists.txt}
• {KEMField,KGeoBag,Kommon}/Documentation/{Reference,CMakeLists.txt}

I think we should move everything to the "main" branch in the "Documentation" folder since there people expect to find documentation and if people look for documentation for an old version of Kassiopeia, there they will look first.

Btw. there exists KEMField/Documentation/manual/manual.pdf which may make sense to link in the documentation as something like "KEMField Developer's Guide". Maybe it can also be compiled to Markdown using Pandoc to integrate it into the main documentation. But I think that's a challenge to solve after the above.

If this is agreed on, here are suggested tasks:

• [x] Forward https://katrin-experiment.github.io to https://katrin-experiment.github.io/Kassiopeia for now
• (Potentially Remove Doxygen-based documentation)
• [x] Combine gh-pages and main:Kassiopeia/Documentation/Reference: #79
• [x] Bring resulting documentation to a reasonably named subdirectory of main:Documentation: #80
• [x] Build GitHub Pages page via Action from main:Documentation: #80
• [x] Remove gh-pages branch -- last commit: https://github.com/KATRIN-Experiment/Kassiopeia/commit/501d247a355d7d8ad1d7df84a40ab9df09240370
• [x] Reference or integrate main:KEMField/Documentation/manual/manual.pdf in the public documentation

[2xB]

One could also add a citation file containing our paper as described in https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files .