Adding the Running SU2 section

Author: EttoreSaetta

_tutorials/compressible_flow/ActuatorDisk_VariableLoad/ActuatorDisk_VariableLoad.md

@@ -219,6 +219,20 @@ The load distribution obtined using the [OptimalPropeller.py](https://github.com
 
 *For reference: Glauert H., Airplane Propellers, in Aerodynamic Theory, Ed. Durand W. F., Vol. IV, pp. 169 - 360, Springer, 1935.*
 
+### Running SU2
+
+The actuator disk with variable load test case is small and will execute relatively quickly on a single workstation or laptop in serial. To run this test case, follow these steps at a terminal command line:
+ 1. Move to the directory containing the configuration file ([propeller_variable_load.cfg](https://github.com/su2code/SU2/tree/master/TestCases/rans/actuatordisk_variable_load/propeller_variable_load.cfg)), the mesh file ([propeller_variable_load.su2](https://github.com/su2code/TestCases/tree/master/rans/actuatordisk_variable_load/propeller_variable_load.su2)) and the propeller input data file ([ActuatorDisk.dat](https://github.com/su2code/SU2/tree/master/TestCases/rans/actuatordisk_variable_load/ActuatorDisk.dat)). Make sure that the SU2 tools were compiled, installed, and that their install location was added to your path.
+ 2. Run the executable by entering 
+ 
+    ```
+    $ SU2_CFD propeller_variable_load.cfg
+    ```
+   
+    at the command line.
+ 3. SU2 will print residual updates with each iteration of the flow solver, and the simulation will terminate after meeting the specified convergence criteria.
+ 4. Files containing the results will be written upon exiting SU2. The flow solution can be visualized in ParaView (.vtk) or Tecplot (.dat for ASCII).
+
 ### Results
 
 Some results for this test case are shown below.