Add acknowledgement about the MRG31k3p implementation.

doc/acknowledgement.txt

@@ -19,3 +19,8 @@ Acknowledgements
   `theano/misc/cpucount.py` come from the project `pyprocessing
   <http://pyprocessing.berlios.de/>`_. It is available under the same license
   as Theano.
+* Our random number generator implementation on CPU and GPU use the MRG31k3p algorithm that is described in:
+
+    P. L'Ecuyer and R. Touzin, `Fast Combined Multiple Recursive Generators with Multipliers of the form a = +/- 2^d +/- 2^e <http://www.informs-sim.org/wsc00papers/090.PDF>`_, Proceedings of the 2000 Winter Simulation Conference, Dec. 2000, 683--689.
+
+  We were autorized by Pierre L'Ecuyer to copy/modify his Java implementation in the `SSJ <http://www.iro.umontreal.ca/~simardr/ssj/>`_ software and to relicense it under BSD 3-Clauses in Theano.