Document use-cases

[This](https://wiki.enablingpersonalizedinterventions.nl/specification/requirements/use_case.html) page still needs to be written, and more importantly, the settings has to be mentioned on [this](https://wiki.enablingpersonalizedinterventions.nl/user-guide/system-admins/installation/worker-node.html) page, as Brane will not properly function without it.