Added notes on benchmark command line argument.

README.rst

@@ -126,7 +126,8 @@ There are optional command line arguments for gprMax:
 
 * ``--geometry-only`` will build a model and produce any geometry views but will not run the simulation. This option is useful for checking the geometry of the model is correct.
 * ``-n`` is used along with a integer number to specify the number of times to run the input file. This option can be used to run a series of models, e.g. to create a B-scan that uses an antenna model.
-* ``-mpi`` is a flag to turn on Message Passing Interface (MPI) task farm functionality. This option is most usefully combined with ``-n`` to allow individual models to be farmed out using MPI. For further details see the Parallel performance section (http://docs.gprmax.com/en/latest/openmp_mpi.html#parallelism-openmp-mpi).
+* ``-mpi`` is a flag to turn on Message Passing Interface (MPI) task farm functionality. This option is most usefully combined with ``-n`` to allow individual models to be farmed out using MPI. For further details see the Parallel performance section (http://docs.gprmax.com/en/latest/openmp_mpi.html).
+* ``-benchmark`` is a flag to turn on benchmarking mode. This can be used to benchmark the threading (parallel) performance of gprMax on different hardware. For further details see the benchmarking section (http://docs.gprmax.com/en/latest/benchmarking.html)
 * ``--write-python`` will write an input file after any Python code blocks in the original input file have been processed.
 * ``-h`` or ``--help`` can be used to get help on command line options.