update instruction on regenerating vocab file

README.md

@@ -91,6 +91,6 @@ This vocabulary is used by Neurobagel APIs to fetch available attributes and att
 When the Neurobagel graph data model is updated (e.g., if new classes or subclasses are created), 
 this file should be regenerated by running:
 ```bash
-python generate_nb_vocab_file.py
+python helper_scripts/generate_nb_vocab_file.py
 ```
 This will create a file called `nb_vocab.ttl` in the current working directory.