add in section on creating worker nodes (docker#51)

Author: Mano Marks

swarm-mode/beginner-tutorial/README.md

@@ -29,6 +29,17 @@ do
 	echo "======> Creating manager$node machine ...";
 	docker-machine create -d virtualbox manager$node;
 done
+```
+
+This second step creates three more machines, and names them worker1, worker2, and worker3
+```
+# This create worker machines
+echo "======> Creating $workers worker machines ...";
+for node in $(seq 1 $workers);
+do
+	echo "======> Creating worker$node machine ...";
+	docker-machine create -d virtualbox worker$node;
+done
 
 # This lists all machines created
 docker-machine ls