message: Add benchmark dashboard link to benchmarks doc. Also, I added a link and
  description for Benchmarks page to Community index page.
diff: # Benchmarks
  -This guide contains instructions for defining and running a TensorFlow benchmark. These benchmarks store output in [TestResults](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/util/test_log.proto) format. If these benchmarks are added to TensorFlow github repo, then we will run them daily with our Jenkins build.
  +This guide contains instructions for defining and running a TensorFlow benchmark. These benchmarks store output in [TestResults](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/util/test_log.proto) format. If these benchmarks are added to TensorFlow github repo, then we will run them daily with our continuous build and display a graph on our dashboard: https://benchmarks-dot-tensorflow-testing.appspot.com/.
  [TOC]
  