fixed readme

README.md

@@ -40,6 +40,7 @@ Please, do not change `OPENAI_EMBEDDINGS_MODEL` value.
 To run the script which builds RAG, you need to launch the following commands:
 ```bash
 pip install -r requirements.txt
+python -m nltk.downloader punkt
 python ./build_rag.py --path_to_dataset Dataset --path_to_index faiss_db
 ```