message: Fix broken link in performance guide
  This fix fixes broken link in performance guide as models repo moved
  slim to `models/research/slim`
  `https://github.com/tensorflow/models/tree/master/slim#Data`
  >
  `https://github.com/tensorflow/models/tree/master/research/slim#Data`
diff: @@ -93,7 +93,7 @@ Reading large numbers of small files significantly impacts I/O performance.
  One approach to get maximum I/O throughput is to preprocess input data into
  larger (~100MB) `TFRecord` files. For smaller data sets (200MB-1GB), the best
  approach is often to load the entire data set into memory. The document
  -[Downloading and converting to TFRecord format](https://github.com/tensorflow/models/tree/master/slim#Data)
  +[Downloading and converting to TFRecord format](https://github.com/tensorflow/models/tree/master/research/slim#Data)
  includes information and scripts for creating `TFRecords` and this
  [script](https://github.com/tensorflow/models/tree/master/tutorials/image/cifar10_estimator/generate_cifar10_tfrecords.py)
  converts the CIFAR-10 data set into `TFRecords`.
  