add a note that --lxc-conf is lxc-driver only.

I'm not looking forward to documenting cli arguments that may or may not show depending on what plugins / drviers you choose

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)


https://groups.google.com/forum/#!topic/docker-user/fOLHkEF2Q1E