tell the user not to run from OSX

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)

docker/docker.go

@@ -98,6 +98,9 @@ func main() {
 	}
 
 	if *flDaemon {
+		if runtime.GOOS != "linux" {
+			log.Fatalf("The Docker daemon is only supported on linux")
+		}
 		if os.Geteuid() != 0 {
 			log.Fatalf("The Docker daemon needs to be run as root")
 		}