Add documentation scenario:bridge

[UJehle]

We should somewhere explain what is the difference between a new bridge and a new road. -> which properties are assumes -> that the differentiation is only important for the routing -> a new “road” in GOAT can be anything – a footpath, a pedestrian zone, a living street, a residential road, etc. -> surface is important for the cycling speed -> wheelchair usability is important for the wheelchair routing

I am just not sure yet, where to put this information. Maybe adding a new chapter to Docs -> Technical Documentation -> "Scenarios"