message: [TF 2.0 docs] Add example for EarlyStopping
  I think a short example like this is very useful for user who don't have much experience and want to use a callback for their first time.
diff: @@ -1018,6 +1018,18 @@ class EarlyStopping(Callback):
  the epoch with the best value of the monitored quantity.
  If False, the model weights obtained at the last step of
  training are used.
  +
  + Example:
  +
  + ```python
  + # first create the callback
  + callback = tf.keras.callbacks.EarlyStopping(monitor='val_loss', patience=3)
  + # this callback will stop training when there is no improvement in
  + # validation loss for three epochs
  + # then simply train the model with the callback
  + model.fit(data, labels, epochs=100, callbacks=[callback],
  + validation_data=(val_data, val_labels))
  + ```
  """
  def __init__(self,
  