Fixes deepset-ai/haystack-core-integrations#726 (#229)

* keyword retrieval example

* keyword retrieval example

* keyword retrieval example

* more explanation

---------

Co-authored-by: Stefano Fiorucci <[email protected]>

integrations/pgvector-documentstore.md

@@ -84,7 +84,7 @@ indexing.run({"converter": {"sources": file_paths}})
 ```
 
 ### Retrieval from PgvectorDocumentStore
-You can retrieve Documents similar to a given query using a simple Pipeline.
+You can retrieve semantically similar documents to a given query using a simple pipeline that includes the `PgvectorEmbeddingRetriever`.
 
 ```python
 from haystack.components.embedders import SentenceTransformersTextEmbedder
@@ -99,6 +99,15 @@ querying.connect("embedder", "retriever")
 results = querying.run({"embedder": {"text": "my query"}})
 ```
 
+You can also retrieve Documents based on keyword matching with the `PgvectorKeywordRetriever`.
+
+```python
+from haystack_integrations.components.retrievers.pgvector import PgvectorKeywordRetriever
+
+retriever = PgvectorKeywordRetriever(document_store=document_store, top_k=3))
+results = retriever.run(query="my query")
+```
+
 ## Examples
 You can find a code example showing how to use the Document Store and the Retriever under the `examples/` folder of [this repo](https://github.com/deepset-ai/haystack-core-integrations/tree/main/integrations/pgvector).