Clarified documentation of ITML (resolves #58) (#59)

Author: Callidior

metric_learn/itml.py

@@ -80,7 +80,8 @@ def fit(self, X, constraints, bounds=None):
     X : (n x d) data matrix
         each row corresponds to a single instance
     constraints : 4-tuple of arrays
-        (a,b,c,d) indices into X, such that d(X[a],X[b]) < d(X[c],X[d])
+        (a,b,c,d) indices into X, with (a,b) specifying positive and (c,d)
+        negative pairs
     bounds : list (pos,neg) pairs, optional
         bounds on similarity, s.t. d(X[a],X[b]) < pos and d(X[c],X[d]) > neg
     """