Update app.py

app.py

@@ -1,6 +1,7 @@
 from langchain.prompts.prompt import PromptTemplate
 from langchain.llms import OpenAIChat
 from langchain.chains import ConversationalRetrievalChain, LLMChain
+from langchain.chains.question_answering import load_qa_chain
 from langchain.embeddings import HuggingFaceEmbeddings, HuggingFaceInstructEmbeddings
 from langchain.callbacks import StdOutCallbackHandler
 from langchain.chains.conversational_retrieval.prompts import CONDENSE_QUESTION_PROMPT