Document that the users can now add new networks without having to reconfigure the host, since the physical network name - i.e. `localnet` attribute of a bridge mapping - can be shared by multiple networks.

The fact that the OVS bridge shared between these networks must accept the VLANs specified in the multiple networks has to be called out. I.e. ensure your OVS bridge uplink is configured as a trunk port, accepting those VLANs.