docs: Update README for PostgreSQL / Cosmos DB Integration (#1576)

Co-authored-by: Pavan Kumar <v-kupavan.microsoft.com>
Co-authored-by: Pavan-Microsoft <v-kupavan@microsoft.com>
Co-authored-by: gpickett <122489228+gpickett@users.noreply.github.com>
Co-authored-by: Prajwal D C <v-dcprajwal@microsoft.com>

README.md

@@ -171,7 +171,7 @@ With the addition of PostgreSQL, customers can leverage the power of a relations
 
 Customers have the option to deploy this solution with PostgreSQL or Cosmos DB. Consider the following when deciding which database to use:
 - PostgreSQL enables a relationship-based AI solution and search indexing for Retrieval Augmented Generation (RAG)
-- Cosmos DB is a NoSQL-based solution for chat history
+- Cosmos DB enables chat history and is a NoSQL-based solution. With Cosmos DB, Azure AI Search is used for storing extracted documents and embeddings.
 
 
 To review PostgreSQL configuration overview and steps, follow the link [here](docs/postgreSQL.md).