message: Fix typo documenation -> documentation
diff: @@ -50,7 +50,7 @@ save files to local directory any more. Note we are also passing the compressed
  files (gzip) as is, since `tensorflow-io` is able to detect and uncompress
  automatically for MNIST dataset if needed.
  -Please check the official [documenation](https://www.tensorflow.org/io) for more
  +Please check the official [documentation](https://www.tensorflow.org/io) for more
  detailed usages.
  ## Installation
  