message: Link to tf.estimator docs for premade estimators.
diff: @@ -177,13 +177,11 @@ other features so you can concentrate on your model. For more details see
  An Estimator is any class derived from @{tf.estimator.Estimator}. TensorFlow
  provides a collection of
  -[pre-made Estimators](https://developers.google.com/machine-learning/glossary/#pre-made_Estimator)
  +@{tf.estimator$pre-made Estimators}
  (for example, `LinearRegressor`) to implement common ML algorithms. Beyond
  those, you may write your own
  -[custom Estimators](https://developers.google.com/machine-learning/glossary/#custom_Estimator).
  -We recommend using pre-made Estimators when just getting started with
  -TensorFlow. After gaining expertise with the pre-made Estimators, we recommend
  -optimizing your model by creating your own custom Estimators.
  +@{$custom_estimators$custom Estimators}.
  +We recommend using pre-made Estimators when just getting started.
  To write a TensorFlow program based on pre-made Estimators, you must perform the
  following tasks:
  