Hard to find documentation on -m mpi4py

[Feng Yu]

Reading through the documentation, there is no specific section on how to launch an MPI application with -m mpi4py, and why -m mpi4py is necessary/preferred than python-mpi executable.

The only relevant example is in Installation under the testing section. I propose adding a section on 'usage' in the documentation.

[Lisandro Dalcin]

Fixed in 337f54d.