Moved RTD badge.

README.rst

@@ -1,12 +1,11 @@
+.. image:: https://readthedocs.org/projects/gprmax/badge/?version=latest
+:target: http://docs.gprmax.com/en/latest/?badge=latest
+:alt: Documentation Status
 
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 Getting Started
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-.. image:: https://readthedocs.org/projects/gprmax/badge/?version=latest
-    :target: http://docs.gprmax.com/en/latest/?badge=latest
-    :alt: Documentation Status
-
 What is gprMax?
 ===============