Document how to setup develop version of QED package

[SimeonEhrig]

For our dev branch version of a QED package we requires, that it is only works together with the dev branch versions of other QED packages.

We should document this and how to setup a dev environment. Maybe we can use the setup_dev_env.jl script.

[SimeonEhrig]

setup_dev_env.jl is not working for this. It is to CI specific. But we could easy write an new script using the major components from setup_dev_env.jl.