Update readme

PiperOrigin-RevId: 265355791

official/mnist/README.md

@@ -12,7 +12,13 @@ APIs.
 ## Setup
 
 To begin, you'll simply need the latest version of TensorFlow installed.
-First make sure you've [added the models folder to your Python path](/official/#running-the-models); otherwise you may encounter an error like `ImportError: No module named official.mnist`.
+First make sure you've [added the models folder to your Python path]:
+
+```shell
+export PYTHONPATH="$PYTHONPATH:/path/to/models"
+```
+
+Otherwise you may encounter an error like `ImportError: No module named official.mnist`.
 
 Then to train the model, run the following: