Update simple_cycles docstring w/ yields and examples (networkx#5709)

Update docstring for simple_cycles.

networkx/algorithms/cycles.py

@@ -111,28 +111,26 @@ def simple_cycles(G):
     G : NetworkX DiGraph
        A directed graph
 
-    Returns
-    -------
-    cycle_generator: generator
-       A generator that produces elementary cycles of the graph.
+    Yields
+    ------
+    list of nodes
        Each cycle is represented by a list of nodes along the cycle.
 
     Examples
     --------
     >>> edges = [(0, 0), (0, 1), (0, 2), (1, 2), (2, 0), (2, 1), (2, 2)]
     >>> G = nx.DiGraph(edges)
-    >>> len(list(nx.simple_cycles(G)))
-    5
+    >>> sorted(nx.simple_cycles(G))
+    [[0], [0, 1, 2], [0, 2], [1, 2], [2]]
 
     To filter the cycles so that they don't include certain nodes or edges,
-    copy your graph and eliminate those nodes or edges before calling
-
-    >>> copyG = G.copy()
-    >>> copyG.remove_nodes_from([1])
-    >>> copyG.remove_edges_from([(0, 1)])
-    >>> len(list(nx.simple_cycles(copyG)))
-    3
+    copy your graph and eliminate those nodes or edges before calling.
+    For example, to exclude self-loops from the above example:
 
+    >>> H = G.copy()
+    >>> H.remove_edges_from(nx.selfloop_edges(G))
+    >>> sorted(nx.simple_cycles(H))
+    [[0, 1, 2], [0, 2], [1, 2]]
 
     Notes
     -----