message: Add example of y_pred as logits tensor case for meanIoU docs
  Documentation added when meanIoU supports y_pred as logits tensor.
diff: @@ -2823,6 +2823,15 @@ class MeanIoU(Metric):
  >>> m.result().numpy()
  0.23809525
  + When passing `y_pred` as a logits tensor:
  +
  + >>> m = tf.keras.metrics.MeanIoU(num_classes=3, from_logits=True)
  + >>> y_true = [2, 0, 1, 1]
  + >>> y_pred = [[2.5, 0.2, 2.7], [-1.4, 0.7, 1.2], [2., 3., 1.4], [2.2, 2.4, 1.5]]
  + >>> m.update_state(y_true, y_pred)
  + >>> m.result().numpy()
  + 0.5
  +
  Usage with `compile()` API:
  ```python
  