Merge pull request #519 from Axelrod-Python/499

Minor: Fixing the hyperlink.

Author: meatballs

docs/citing_the_library.rst

@@ -5,5 +5,6 @@ We would be delighted if anyone wanted to use and/or reference this library for
 their own research.
 
 If you do please let us know and reference the library: as described in the
-[CITATION.txt file on the library
-repository](https://github.com/Axelrod-Python/Axelrod/blob/master/CITATION.txt).
+`CITATION.txt file on the library
+repository
+<https://github.com/Axelrod-Python/Axelrod/blob/master/CITATION.txt>`_.