Update docs for 2G memory default
Update docs for 2G memory default

Docker-DCO-1.1-Signed-off-by: Glyn Normington <gnormington@gopivotal.com> (github: glyn)

moxiegirl/boot2docker-cli,tianon/boot2docker-cli,beni55/boot2docker-cli,SvenDowideit/boot2docker-cli,boot2docker/boot2docker-cli,vmware/boot2docker-cli,mattrobenolt/boot2docker-cli,nathanleclaire/boot2docker-cli,tianon/boot2docker-cli,SvenDowideit/boot2docker-cli,nathanleclaire/boot2docker-cli,vmware/boot2docker-cli,mattrobenolt/boot2docker-cli,moxiegirl/boot2docker-cli,beni55/boot2docker-cli,boot2docker/boot2docker-cli