Update naming.html to reflect all valid IPSources values

[gkleiman]

From http://mesosphere.github.io/mesos-dns/docs/naming.html:

Note: Container IPs must be provided by the executor of a task in one of the following task status labels:

Docker.NetworkSettings.IPAddress
MesosContainerizer.NetworkSettings.IPAddress.
``

Container IPs can also be taken from NetworkInfo, the doc should be updated to reflect that.