Add note about dumb VPNs.
Add note about dumb VPNs.

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