clarified difference between v4 and v3 service installation

After upgrading from v3 to v4, our service install scripts were not creating the right queue names even though we were specifying the /serviceName when doing an NServiceBus /install.  We had to add /endpointName to get it to take the right name.

I think this relates to eripe970's comment that the documentation is wrong in https://github.com/Particular/NServiceBus/issues/1816 although he explained his problem differently than mine.