Update README.md

README.md

@@ -30,8 +30,10 @@ embeddings = model(input_ids).pooler_output
 You can use it using `haystack` as follows:
 
 ```
-from haystack.retriever.dense import DensePassageRetriever
-retriever = DensePassageRetriever(document_store=document_store,
+from haystack.nodes import DensePassageRetriever
+from haystack.document_stores import InMemoryDocumentStore
+
+retriever = DensePassageRetriever(document_store=InMemoryDocumentStore(),
                                   query_embedding_model="firqaaa/indo-dpr-passage_encoder-single-squad-base",
                                   passage_embedding_model="firqaaa/indo-dpr-passage_encoder-single-squad-base",
                                   max_seq_len_query=64,