Streamline introduction.md of luscious-lasagna

[senekor]

Many topics that were covered previously are not relevant to the actual tasks, they should be covered in a separate exercise.

This was discussed here.

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[senekor]

The team effort to get the syllabus in a good shape again died down. I'm keeping this open in case it is useful at some point, but I think future work on the syllabus should not hesitate to close this and do something new from scratch.