message: Clarifies the purpose to use a fn to create retrieve embedding ops.
diff: @@ -836,6 +836,19 @@ class TPUEmbedding(object):
  slot_variable_names_by_table=None):
  """Create embedding and slot variables, with ops to load and retrieve them.
  + N.B.: the retrieve embedding variables (including slot variables) ops are
  + returned as lambda fn, as the call side might want to impose control
  + dependencies between the TPU computation and retrieving actions. For
  + example, the following code snippet ensures the TPU computation finishes
  + first, and then we pull the variables back from TPU to CPU.
  +
  + ```
  + updates_ops = []
  + with ops.control_dependencies([loss]):
  + for op_fn in retrieve_parameters_op_fns:
  + update_ops.append(op_fn())
  + ```
  +
  Args:
  embedding_variable_name_by_table: A dictionary mapping from string of
  table name to string of embedding variable name. If `None`,
  