Update doc in classifiers

(cherry picked from commit 9e341f7)

Author: Irina Nicolae

art/classifiers/classifier.py

@@ -3,6 +3,8 @@
 import abc
 import sys
 
+# TODO Add tests for defences on classifier
+
 # Ensure compatibility with Python 2 and 3 when using ABCMeta
 if sys.version_info >= (3, 4):
     ABC = abc.ABC
@@ -20,6 +22,8 @@ def __init__(self, clip_values, defences=None):
         :param clip_values: Tuple of the form `(min, max)` representing the minimum and maximum values allowed
                for features.
         :type clip_values: `tuple`
+        :param defences: Defences to be activated with the classifier.
+        :type defences: `str` or `list(str)`
         """
         self._clip_values = clip_values
         self._parse_defences(defences)

art/classifiers/keras.py

@@ -18,8 +18,10 @@ def __init__(self, clip_values, model, use_logits=False, defences=None):
         :type clip_values: `tuple`
         :param model: Keras model
         :type model: `keras.models.Sequential`
-        :param use_logits: True if the output of the model are the logits
+        :param use_logits: True if the output of the model are the logits.
         :type use_logits: `bool`
+        :param defences: Defences to be activated with the classifier.
+        :type defences: `str` or `list(str)`
         """
         import keras.backend as k