added an allgather example because I couldn't find one online for some reason

Author: jjmaldonis

allgather_example.py

@@ -0,0 +1,8 @@
+from mpi4py import MPI
+
+rank = MPI.COMM_WORLD.Get_rank()
+print("I am rank {} of {}".format(rank, MPI.COMM_WORLD.Get_size()))
+
+ranks = MPI.COMM_WORLD.allgather(rank)
+
+print(ranks)