A simple example added

LICENSE

+MIT License
+
+Copyright (c) 2019-present, Stanislav Bohm
+
+Permission is hereby granted, free of charge, to any person
+obtaining a copy of this software and associated documentation
+files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.

examples/twotasks/twotasks.py

+#
+# The following example submits two MPI tasks
+#  - The first one takes no parameters, runs on 1 node and produces 4 outputs
+#  - The second one runs on 4 nodes, takes a configuration (the same for each process)
+#    and each MPI rank gets 1 output from task 1.
+#
+#
+#    /---------------------------\
+#    | Task 1 (my_preprocessing) |
+#    |---------------------------|
+#    | Rank 0                    |
+#    | Out1 Out2 Out3 Out4       |
+#    \---------------------------/
+#        |   |    |    \----------------\
+#        |   |    |                     |
+#        |   |    \----------\          |
+#        |   |               |          |
+#        |   \-----\         |          |
+#        v         v         v          v
+#    /---------------------------------------\
+#    | Task 2 (my_computation)               |
+#    |---------------------------------------|
+#    | Rank 0  | Rank 1  | Rank 0  | Rank 0  |
+#    \---------------------------------------/
+
+
+import quake.client as quake
+
+
+@quake.mpi_task(n_processes=1, n_outputs=4)
+def my_preprocessing():
+    # Let us produce 4 pieces of something in a simple MPI application with 1 process
+    return ["something1", "something2", "something3", "something4"]
+
+
+@quake.mpi_task(n_processes=4)
+@quake.arg("my_data", layout="scatter")
+def my_computation(my_config, my_data):
+    # This is called in 4 MPI processes
+    from mpi4py import MPI
+
+    comm = MPI.COMM_WORLD
+    rank = comm.Get_rank()
+    return "Computation at rank {}: configuration={}, data={}".format(
+        rank, my_config, my_data
+    )
+
+
+# Creating a plan
+
+data = my_preprocessing()
+computation = my_computation("my_configuration", data)
+
+
+# Submitting the plan & waiting for results
+
+result = quake.gather(computation)
+
+for i, r in enumerate(result):
+    print("Output {}: {}".format(i, r))
+
+#  The expected output:
+#  Output 0: Computation at rank 0: configuration=my_configuration, data=something1
+#  Output 1: Computation at rank 1: configuration=my_configuration, data=something2
+#  Output 2: Computation at rank 2: configuration=my_configuration, data=something3
+#  Output 3: Computation at rank 3: configuration=my_configuration, data=something4