Fix in Docs to address question asked in issue 4182 (#4204)

Added compute comment and changed DiGraph to Graph(directed=True)
Tested in a notebook.

Addresses question in #4182

Authors:
  - Don Acosta (https://github.com/acostadon)

Approvers:
  - Brad Rees (https://github.com/BradReesWork)

URL: #4204

docs/cugraph/source/api_docs/cugraph/dask-cugraph.rst

@@ -60,12 +60,15 @@ Example
     )
 
     # create graph from input data
-    G = cugraph.DiGraph()
+    G = cugraph.Graph(directed=True)
     G.from_dask_cudf_edgelist(e_list, source='src', destination='dst')
 
     # run PageRank
     pr_df = dask_cugraph.pagerank(G, tol=1e-4)
 
+    # need to call compute to generate results
+    pr_df.compute()
+
     # cluster clean up
     Comms.destroy()
     client.close()