Trying to follow the development instructions is confusing

### Aktuelles Verhalten

Wanting to set up a new local development environment directs me both to development/doc/setup.md and doc/development, which do not describe the same steps. Which one is correct?

I chose to follow the development repo, where I'm asked to declare an $INSTANCE_NAME - which is _not_ something arbitrary, but has to be a specific value, referencing something (a wagon, I assume). This is not explained.

### Gewünschtes Verhalten

Setting up a dev env is a clearly defined process without contradictions and under-defined terms.

### Schritte zu reproduzieren

Try and set up a dev environment starting from the Hitobito repository on Github.

### Wann ist der Fehler aufgetreten?

_No response_

### hitobito version

_No response_

### Organisation

_No response_

### Screenshots, weiterer Kontext

_No response_

### ToDos

_No response_