message: Update docstring for keras.layers.Activation
diff: @@ -363,9 +363,20 @@ class Activation(Layer):
  activation: Activation function, such as `tf.nn.relu`, or string name of
  built-in activation function, such as "relu".
  + Usage:
  +
  + >>> layer = tf.keras.layers.Activation('relu')
  + >>> output = layer([-3.0, -1.0, 0.0, 2.0])
  + >>> list(output.numpy())
  + [0.0, 0.0, 0.0, 2.0]
  + >>> layer = tf.keras.layers.Activation(tf.nn.relu)
  + >>> output = layer([-3.0, -1.0, 0.0, 2.0])
  + >>> list(output.numpy())
  + [0.0, 0.0, 0.0, 2.0]
  +
  Input shape:
  Arbitrary. Use the keyword argument `input_shape`
  - (tuple of integers, does not include the samples axis)
  + (tuple of integers, does not include the batch axis)
  when using this layer as the first layer in a model.
  Output shape:
  