message: Add version to image retraining setup instructions.
  fixes:
diff: @@ -44,8 +44,14 @@ following command (these examples are not included in the installation):
  ```sh
  git clone https://github.com/tensorflow/tensorflow
  +```
  +
  +Then checkout the version of the tensorflow repository matching your
  +installation and this tutorial as follows:
  +``` sh
  cd tensorflow
  +git checkout {version}
  ```
  In the simplest cases the retrainer can then be run like this:
  