Add extra newline between images.

README.rst

@@ -2,6 +2,7 @@
     :target: http://docs.gprmax.com/en/latest/?badge=latest
     :alt: Documentation Status
 
+
 .. image:: https://github.com/gprMax/gprMax/blob/master/docs/source/images/gprMax_logo_small.png
     :target: http://www.gprmax.com