Update documentation to reflect new taskfarm flag

README.rst

@@ -171,7 +171,7 @@ Argument name          Type      Description
 ====================== ========= ===========
 ``-n``                 integer   Number of required simulation runs. This option can be used to run a series of models, e.g. to create a B-scan with 60 traces: ``(gprMax)$ python -m gprMax examples/cylinder_Bscan_2D.in -n 60``
 ``-i``                 integer   Model number to start/restart the simulation from. It would typically be used to restart a series of models from a specific model number, with the n argument, e.g. to restart from A-scan 45 when creating a B-scan with 60 traces.
-``-mpi``               integer   number of Message Passing Interface (MPI) tasks, i.e. master + workers, for MPI task farm. This option is most usefully combined with ``-n`` to allow individual models to be farmed out using an MPI task farm, e.g. to create a B-scan with 60 traces and use MPI to farm out each trace: ``(gprMax)$ python -m gprMax examples/cylinder_Bscan_2D.in -n 60 -mpi 61``. For further details see the `parallel performance section of the User Guide <http://docs.gprmax.com/en/latest/openmp_mpi.html>`_
+``-taskfarm``          integer   number of Message Passing Interface (MPI) tasks, i.e. master + workers, for MPI task farm. This option is most usefully combined with ``-n`` to allow individual models to be farmed out using an MPI task farm, e.g. to create a B-scan with 60 traces and use MPI to farm out each trace: ``(gprMax)$ python -m gprMax examples/cylinder_Bscan_2D.in -n 60 -taskfarm 61``. For further details see the `parallel performance section of the User Guide <http://docs.gprmax.com/en/latest/openmp_mpi.html>`_
 ``-gpu``               list/bool Flag to use NVIDIA GPU or list of NVIDIA GPU device ID(s) for specific GPU card(s), e.g. ``-gpu 0 1``
 ``-opencl``            list/bool Flag to use OpenCL or list of OpenCL device ID(s) for specific compute device(s).
 ``--geometry-only``    flag      Build a model and produce any geometry views but do not run the simulation, e.g. to check the geometry of a model is correct: ``(gprMax)$ python -m gprMax examples/heterogeneous_soil.in --geometry-only``