Update app.py

app.py

@@ -705,6 +705,8 @@ bm25_index = BM25Index.build_from_documents(
       documents=iter(sciq.corpus),
       ndocs=12160,
       show_progress_bar=True,
+      k1=best_k1,
+      b=best_b
   )
 bm25_index.save("output/bm25_index")
 bm25_retriever = BM25Retriever(index_dir="output/bm25_index")