Add bash completion for `dockerd --experimental`

Signed-off-by: Harald Albers <github@albersweb.de>

contrib/completion/bash/docker

@@ -1729,6 +1729,7 @@ _docker_daemon() {
 	local boolean_options="
 		$global_boolean_options
 		--disable-legacy-registry
+		--experimental
 		--help
 		--icc=false
 		--ip-forward=false