networking.md: Networking between containers works without ip_forward

My test setup here starts docker with --ip-forward=false --iptables=false. I start two containers on the default docker0 bridge. I have no problems pinging container#1 from container#2, with /proc/sys/net/ipv4/ip_forward set to 0. Which is as expected, since you add all containers to the same bridge by default.

ip_forward is only needed for talking to ip addresses not on the bridge subnet, such as the wider world via nat.

usually not necessary because the Docker package does it when its installed.