[TF 2.0 docs] Add example for EarlyStopping

tensorflow/python/keras/callbacks.py

@@ -1018,6 +1018,16 @@ 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
+  callback = tf.keras.callbacks.EarlyStopping(monitor='val_loss', patience=3)
+  # This callback will stop the training when there is no improvement in
+  # the validation loss for three consecutive epochs.
+  model.fit(data, labels, epochs=100, callbacks=[callback], 
+      validation_data=(val_data, val_labels))
+  ```
   """
 
   def __init__(self,