adding attribution for original source code

Author: perimosocordiae

metric_learn/itml.py

@@ -9,6 +9,8 @@
 incorporate a prior on the distance function.
 Unlike some other methods, ITML does not rely on an eigenvalue computation
 or semi-definite programming.
+
+Adapted from Matlab code at http://www.cs.utexas.edu/users/pjain/itml/
 """
 
 from __future__ import print_function, absolute_import