Update usingdocker.md

boot2docker on windows also uses an IP of its own.

Docker-DCO-1.1-Signed-off-by: Tom Maaswinkel <tom.maaswinkel@12wiki.eu> (github: SvenDowideit)
expand to 'used b2d vm on any of the platforms'

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
convert OSX into OS X

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Merge pull request #6789 from SvenDowideit/pr_out_expand_to_used_b2d_vm_on_any_of_the_platforms

expand to 'used b2d vm on any of the platforms'