Adding introduction.py

examples/introduction.py

+from b_asic.core_operations import Addition, ConstantMultiplication
+from b_asic.signal_flow_graph import SFG
+from b_asic.special_operations import Delay, Input, Output
+
+i = Input()
+d = Delay()
+o = Output(d)
+c = ConstantMultiplication(0.5, d)
+a = Addition(i, c)
+d.input(0).connect(a)
+
+sfg = SFG([i], [o])