Documented --storage-opt=[] option in man 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: aa00ad47e243b41b863354e6360a5d3a46aa3212
Component: engine