Added some info on benchmarking.

docs/source/benchmarking.rst

@@ -15,7 +15,7 @@ The following simple model is an example (found in the ``tests/benchmarking`` su
     :language: none
     :linenos:
 
-
+The ``#num_threads`` command should be adjusted from 1 up to the number of physical CPU cores on your machine, the model run, and the solving time recorded.
 
 
 Results
@@ -24,7 +24,12 @@ Results
 Mac OS X
 --------
 
+iMac (Retina 5K, 27-inch, Late 2014), Mac OS X 10.11.3
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 .. figure:: ../../tests/benchmarking/results/MacOSX/Darwin-15.3.0-x86_64-i386-64bit.png
     :width: 600px
 
-    Execution time and speed-up factor plots for gprMax (v3b21) and GprMax (v2).
+    Execution time and speed-up factor plots for gprMax (v3b21) and GprMax (v2).
+
+The results demonstrate that the new (v3) code written in Python and Cython is faster, in these two benchmarks, that the old (v2) code which was written in C. It also shows that the performance scaling with multiple OpenMP threads is better with the old (v2) code.