Added mention of 'inputdirectory' variable available for Python scripting.

docs/source/python_scripting.rst

@@ -11,15 +11,16 @@ Constants/variables
 
 You can access the following built-in constants from your Python code:
 
-* ``c`` which is the speed of light in vacuum :math:`c=2.9979245 \times 10^8` m/s
-* ``e0`` which is the permittivity of free space :math:`\epsilon_0=8.854187 \times 10^{-12}` F/m
-* ``m0`` which is the permeability of free space :math:`\mu_0=1.256637 \times 10^{-6}` H/m
-* ``z0`` which is the impedance of free space :math:`z_0=376.7303134` Ohms
+* ``c`` is the speed of light in vacuum :math:`c=2.9979245 \times 10^8` m/s
+* ``e0`` is the permittivity of free space :math:`\epsilon_0=8.854187 \times 10^{-12}` F/m
+* ``m0`` is the permeability of free space :math:`\mu_0=1.256637 \times 10^{-6}` H/m
+* ``z0`` is the impedance of free space :math:`z_0=376.7303134` Ohms
 
 You can access the following built-in variables from your Python code:
 
-* ``current_model_run`` which is the current run number of the model that is been executed.
-* ``number_model_runs`` which is the total number of runs specified when the model was initially executed, i.e. from ``python -m gprMax my_input_file -n number_of_model_runs``
+* ``current_model_run`` is the current run number of the model that is been executed.
+* ``number_model_runs`` is the total number of runs specified when the model was initially executed, i.e. from ``python -m gprMax my_input_file -n number_of_model_runs``
+* ``inputdirectory`` is the path to the directory where your input file is located.
 
 Antenna models
 ==============