Set a proper structure for the tutorial

At the moment, the updated docs can be found within the `docs/` folder. I think we can add the other docs within this directory and update the information or remove the deprecated information. When building the docs, we can see that the tutorial structure is kind of messy so we can define a proper structure here and implement it once decided.

Start by reviewing the existing material in the docs/ folder and building the documentation to see how the tutorial is currently organized. Identify deprecated information and the docs that should be added or updated, then propose a structure before implementing it. Done means the tutorial has an agreed, coherent structure and the documentation reflects it.

Vom Indexierungsmodell aus dem Issue-Text verfasst.