Switch documentation access in Jupyter notebooks to @doc as to ensure compatibility with VS Code

[gwr-de]

In the lecture notebooks, ?command is used to access the documentation within Juptyer notebooks. Unfortunately, this will not work out when the notebooks are run from within Visual Studio Code, which has many advantages and imo is the most often used IDE for Julia.

I would suggest that you change this to @doc command in the notebooks, which will work out in VS Code as well (note that one currently needs to switch output presentation from LaTeX to Markdown in VS Code due to issues with the verbatim environment).