Note that using -lxc-conf to change things Docker manages has pitfalls

Signed-off-by: Sven Dowideit <SvenDowideit@docker.com>

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Merge pull request #9493 from SvenDowideit/note-lxc-conf-pitfall

Note that using -lxc-conf to change things Docker manages has pitfalls