message: added link to benchmarks in community page
diff: @@ -10,3 +10,5 @@ This section contains the following documents:
  TensorFlow source code or documentation, please read this guide.
  * @{$style_guide$TensorFlow Style Guide}, which identifies coding style
  conventions that TensorFlow developers and users should follow.
  + * @{$benchmarks$Benchmarks}, Benchmarks, a guide for defining and
  + running a TensorFlow benchmark.
  