message: Add Estimator release notes.
diff: @@ -41,6 +41,7 @@ Because of [issues with building on windows](https://github.com/tensorflow/tenso
  * Fix issue where GRU would crash or give incorrect output when a `tf.distribute.Strategy` was used.
  * `tf.estimator`
  * Added option in `tf.estimator.CheckpointSaverHook` to not save the `GraphDef`.
  + * Moving the checkpoint reader from swig to pybind11.
  * `tf.keras`
  * Export depthwise_conv2d in `tf.keras.backend`.
  * In Keras Layers and Models, Variables in `trainable_weights`, `non_trainable_weights`, and `weights` are explicitly deduplicated.
  