Initialize DiGraphMatcher.
G1 and G2 should be nx.Graph or nx.MultiGraph instances.
Examples
To create a GraphMatcher which checks for syntactic feasibility:
>>> G1 = nx.DiGraph(nx.path_graph(4, create_using=nx.DiGraph()))
>>> G2 = nx.DiGraph(nx.path_graph(4, create_using=nx.DiGraph()))
>>> DiGM = nx.DiGraphMatcher(G1,G2)