Moved RTD badge.

README.rst

@@ -1,6 +1,6 @@
 .. image:: https://readthedocs.org/projects/gprmax/badge/?version=latest
-:target: http://docs.gprmax.com/en/latest/?badge=latest
-:alt: Documentation Status
+    :target: http://docs.gprmax.com/en/latest/?badge=latest
+    :alt: Documentation Status
 
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 Getting Started