message: Update sparse input documentation.
diff: @@ -218,7 +218,9 @@ def Input( # pylint: disable=invalid-name
  dtype: The data type expected by the input, as a string
  (`float32`, `float64`, `int32`...)
  sparse: A boolean specifying whether the placeholder to be created is
  - sparse. Only one of 'ragged' and 'sparse' can be True.
  + sparse. Only one of 'ragged' and 'sparse' can be True. Note that,
  + if `sparse` is False, sparse tensors can still be passed into the
  + input - they will be densified with a default value of 0.
  tensor: Optional existing tensor to wrap into the `Input` layer.
  If set, the layer will not create a placeholder tensor.
  ragged: A boolean specifying whether the placeholder to be created is
  