Fix usage.sh?

examples/usage.sh

@@ -23,7 +23,14 @@ head -n 20 output.xyz
 
 metatensor-models eval --help
 
-# For example, the following command
+# However, before we export the model, we need to run the following command to
+# set up the environment for exporting
+
+python ../scripts/setup.py
+
+# The above script can be found in the `scripts` folder of the repository.
+
+# Finally, the `metatestor-models export`, i.e.,
 
 metatensor-models export model.pt