DOC add a comment to explain fit/transform in the user guide example
@@ -69,6 +69,7 @@ newly transformed sample matrix ``X``::
>>> from sklearn.preprocessing import StandardScaler
>>> X = [[0, 15],
... [1, -10]]
+ >>> # scale data according to computed scaling values
>>> StandardScaler().fit(X).transform(X)
array([[-1., 1.],
[ 1., -1.]])
