[Software architect] Pick a requirements file and put it in the `design` folder

[richelbilderbeek]

Currently, some of us have written a requirements file, e.g. https://github.com/programming-formalisms/programming_formalisms_project_summer_2024/blob/main/learners/fabio/requirements.md

However, for a shared project, we need to pick one.

Pick a requirements file and put it at design/requirements.md. You may also rewrite it.

When done:

• [ ] Create one or more Issues per requirement