chore(readme): add Quick demo section with video, update how it works outputs

cmd/uncloud/machine/add.go

@@ -98,6 +98,7 @@ func add(ctx context.Context, uncli *cli.CLI, remoteMachine cli.RemoteMachine, o
 
 	// Wait for the cluster to be initialised to be able to deploy the Caddy service.
 	fmt.Println("Waiting for the machine to be ready...")
+	fmt.Println()
 	if err = waitClusterInitialised(ctx, machineClient); err != nil {
 		return fmt.Errorf("wait for cluster to be initialised on machine: %w", err)
 	}

cmd/uncloud/machine/init.go

@@ -121,6 +121,7 @@ func initCluster(ctx context.Context, uncli *cli.CLI, remoteMachine *cli.RemoteM
 	// The creation of a deployment plan talks to cluster API. Since the API needs a few moments to become available
 	// after cluster initialisation, we keep the user informed during this wait.
 	fmt.Println("Waiting for the machine to be ready...")
+	fmt.Println()
 
 	if !opts.noDNS {
 		domain, err := client.ReserveDomain(ctx, &pb.ReserveDomainRequest{Endpoint: opts.dnsEndpoint})