Update README to make Debian default OS
Update README to make Debian default OS

RickyCook/DockCI,RickyCook/DockCI,sprucedev/DockCI,sprucedev/DockCI-Agent,sprucedev/DockCI,sprucedev/DockCI,RickyCook/DockCI,sprucedev/DockCI-Agent,sprucedev/DockCI,RickyCook/DockCI