doc(README): Have the user pass '-v' when starting marconi-server

Users sometimes get confused when maconi-server doesn't print out anything
about which IP and port it is listening on. Recommend passing '-v' so they
learn this trick right off the bat.

Change-Id: I49cd29566b18506fad4f9450ba46159f0a75590d
Merge "doc(README): Have the user pass '-v' when starting marconi-server"