Improve error when connecting service to network

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Signed-off-by: Ben Firshman <ben@firshman.co.uk>

daemon/cluster/cluster.go

@@ -1764,7 +1764,7 @@ func (c *Cluster) populateNetworkID(ctx context.Context, client swarmapi.Control
 		apiNetwork, err := getNetwork(ctx, client, n.Target)
 		if err != nil {
 			if ln, _ := c.config.Backend.FindNetwork(n.Target); ln != nil && !ln.Info().Dynamic() {
-				err = fmt.Errorf("network %s is not eligible for docker services", ln.Name())
+				err = fmt.Errorf("The network %s cannot be used with services. Only networks scoped to the swarm can be used, such as those created with the overlay driver.", ln.Name())
 				return apierrors.NewRequestForbiddenError(err)
 			}
 			return err