message: Flesh out the docstring for the PreprocessingLayer class.
diff: @@ -52,6 +52,18 @@ keras_kpl_gauge = monitoring.BoolGauge(
  class PreprocessingLayer(Layer):
  """Base class for Preprocessing Layers.
  + **Don't use this class directly: it's an abstract base class!** You may
  + be looking for one of the many built-in
  + [preprocessing layers](https://keras.io/guides/preprocessing_layers/)
  + instead.
  +
  + Preprocessing layers are layers whose state gets computed before model
  + training starts. They do not get updated during training.
  + Most preprocessing layers implement an `adapt()` method for state computation.
  +
  + The `PreprocessingLayer` class is the base class you would subclass to
  + implement your own preprocessing layers.
  +
  Attributes:
  stateful: Whether the layer contains state that needs to be adapted via
  `PreprocessingLayer.adapt`.
  