message: Add usage example to tf.keras.utils.to_categorical
diff: @@ -27,6 +27,11 @@ def to_categorical(y, num_classes=None, dtype='float32'):
  E.g. for use with categorical_crossentropy.
  + Usage Example:
  + >>> y = [0, 1, 2, 3]
  + >>> tf.keras.utils.to_categorical(y, num_classes=4)
  + array([...], dtype=float32)
  +
  Arguments:
  y: class vector to be converted into a matrix
  (integers from 0 to num_classes).
  