Test large version of logo for doc building.

README.rst

@@ -2,7 +2,8 @@
     :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.png
+    :target: http://www.gprmax.com
 
 ***************
 Getting Started