First reasonable exercises

See merge request !12

More stuff for the exercise

See merge request !11

Update SUMMARY.md

See merge request !10

Develop

See merge request !9

Grundlagen danetro SoSe 21

See merge request !8

# Conflicts:
#   SUMMARY.md

Update stuff

See merge request !7

only stubs by now.

with still missing a number of contents.

still not yet there.