Add LangChain QA example with context

Author: gustavocidornelas

examples/llms/langchain/question-answering-with-context/requirements.txt

@@ -0,0 +1,7 @@
+chroma-hnswlib==0.7.3
+chromadb==0.4.13
+faiss-cpu==1.7.4
+langchain==0.0.302
+openai==0.28.1
+pandas==2.0.3
+tiktoken==0.5.1