Documented --storage-opt=[] option in cli reference page. Content taken from: daemon/graphdriver/devmapper/README.md Signed-off-by: Michal Minar <miminar@redhat.com> Docker-DCO-1.1-Signed-off-by: Michal Minar <miminar@redhat.com> (github: SvenDowideit) Upstream-commit: a2aa78f6ec9e0a654f92c57336f8e487477d4040 Component: engine