message: Clarify meaning of `num_sampled` in `nce_loss`.
  Fixes
diff: @@ -1210,7 +1210,9 @@ def nce_loss(weights,
  num_true]`. The target classes.
  inputs: A `Tensor` of shape `[batch_size, dim]`. The forward
  activations of the input network.
  - num_sampled: An `int`. The number of classes to randomly sample per batch.
  + num_sampled: An `int`. The number of negative classes to randomly sample
  + per batch. This single sample of negative classes is evaluated for each
  + element in the batch.
  num_classes: An `int`. The number of possible classes.
  num_true: An `int`. The number of target classes per training example.
  sampled_values: a tuple of (`sampled_candidates`, `true_expected_count`,
  