Need update README example.

Need change l1.SetSpt(1232) to l1.SetSPt(1232), and fmt.Printf("dst=%v spt=%v src=%v\n", l2.Dst(), l2.Spt(), l2.Src()) to fmt.Printf("dst=%v spt=%v src=%v\n", l2.Dst(), l2.SPt(), l2.Src())