Update contributors to include a link to the contributors graph

CONTRIBUTORS.rst

@@ -6,3 +6,9 @@ The core contributors for Pinry have been/currently are:
 * Isaac Bythewood <http://isaacbythewood.com/>
 * Krzysztof Klimonda
 
+For a full list of contributors check out the `GitHub Contributors Graph`_.
+
+.. Links
+
+.. _GitHub Contributors Graph: https://github.com/pinry/pinry/graphs/contributors
+