message: Add more details to NMS docstring to describe what input boxes are valid.
diff: @@ -4689,7 +4689,11 @@ def non_max_suppression_padded_v2(boxes,
  Args:
  boxes: a tensor of rank 2 or higher with a shape of [..., num_boxes, 4].
  - Dimensions except the last two are batch dimensions.
  + Dimensions except the last two are batch dimensions. The last dimension
  + represents box coordinates, given as [y_1, x_1, y_2, x_2]. The coordinates
  + on each dimension can be given in any order
  + (see also `canonicalized_coordinates`) but must describe a box with
  + a positive area.
  scores: a tensor of rank 1 or higher with a shape of [..., num_boxes].
  max_output_size: a scalar integer `Tensor` representing the maximum number
  of boxes to be selected by non max suppression.
  