Update README now that -x works for IPv4.
Update README now that -x works for IPv4.

tcatm/babeld,Gwendocg/babeldToS,wlanslovenija/babeld,Gwendocg/babeldToS,jech/babeld,sudomesh/babeld,jech/babeld,wlanslovenija/babeld,boutier/babeld,Drooids/babeld,dtaht/babeld-shortrtt-metrics,woniullb/babeld