Tidied some of the text.

docs/source/screencasts.rst

@@ -11,9 +11,9 @@ Installation
 
 * `How to install gprMax for end users on Microsoft Windows <https://youtu.be/dvC0_7qFVbE>`_ -- Needs updating for new unified installation procedure (30/05/2016)
 
-Wave propagation
-----------------
+Visualising EM wave propagation
+-------------------------------
 
-Using the ``#snapshot`` command and Paraview to visualise how the electromagnetic waves are propagating in a simulation.
+You can use the ``#snapshot`` command and Paraview to visualise how electromagnetic waves propagate in a simulation.
 
 * `PEC cylinder buried in a lossless half-space <https://youtu.be/BpBo0-SFda4>`_