Mosquitto: Improve prerequisites

_@michaelkremmel reported this the other day about the [basic MQTT tutorial](https://cratedb.com/docs/guide/integrate/mqtt/tutorial.html). Thank you._

## Pitch

I think the prerequisites could be a bit more substantial. The other compenents like Mosquitto and Lorry Stream are linked above, but not in the prerequisites. Docker is not linked at all, and depending how lorrystream is used you need python and pip as well. But it is also needed for crash and crash is not even mentioned (outside of the specific commands).