message: added usage example and errors raised
diff: @@ -36,6 +36,17 @@ def to_categorical(y, num_classes=None, dtype='float32'):
  Returns:
  A binary matrix representation of the input. The classes axis is placed
  last.
  +
  + Usage Example:
  + ```python
  + import tensorflow as tf
  + y = [0, 2, 4, 3, 5, 0, 1, 1, 2]
  + tf.keras.utils.to_categorical(y, 6)
  + ```
  +
  + Raises:
  + Value Error: If input contains string value
  +
  """
  y = np.array(y, dtype='int')
  input_shape = y.shape
  