Improve the documentation for AI search. (Azure#53368)

Author: nick863

sdk/ai/Azure.AI.Agents.Persistent/samples/Sample14_PersistentAgents_Azure_AI_Search.md

@@ -125,7 +125,7 @@ Assert.AreEqual(
     run.LastError?.Message);
 ```
 
-4. In our search we have used an index containing "embedding", "token", "category" and also "title" fields. This allowed us to get reference title and url. In the code below, we iterate messages in chronological order and replace the reference placeholders by url and title.
+4. In our search we have used an index containing "embedding", "token", "category", "title" and "url" fields as shown in the image. ![Sample index](images/sample_index.png) The last two fields are needed to get citation title and url, retrieved by the agent. In the code below, we iterate messages in chronological order and replace the reference placeholders by url and title.
 
 Synchronous sample:
 ```C# Snippet:AgentsPopulateReferencesAgentWithAzureAISearchTool_Sync