message: Clarify a caveat about metrics.
diff: @@ -116,7 +116,8 @@ in the input function gives a solid boost in performance. When using
  ## Caveats
  This feature is in early stages and there are a lot of improvements forthcoming:
  -* Metrics are not yet supported during distributed training.
  +* Metrics are not yet supported during distributed training. They are still
  +supported during the evaluation.
  * Summaries are only computed in the first tower in `MirroredStrategy`.
  * Evaluation is not yet distributed.
  * Eager support is in the works; performance can be more challenging with eager
  