Now that docker sets /proc/sys/net/ipv4/ip_forward by default, remove
the step to enable it in the installation docs.
Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
An additional flag to limit the networking MTU is required in three Compute Engine zones for reliable networking from inside the docker container. Added a warning to that effect to the QuickStart guide.