Update main.py

main.py

@@ -18,6 +18,7 @@ from langchain.callbacks.base import BaseCallbackHandler
 from langchain.chains import (
     StuffDocumentsChain, LLMChain, ConversationalRetrievalChain
 )
+from langchain_core.prompts import PromptTemplate
 import chainlit as cl
 from chainlit.input_widget import TextInput, Select, Switch, Slider
 @cl.password_auth_callback