Add a welcome message

Signed-off-by: David Gageot <david.gageot@docker.com>

Author: dgageot

examples/rag.yaml

@@ -8,6 +8,7 @@ agents:
       can use when it makes sense to do so, based on the user's question.
       If you receive sources from the knowledge base, always include them as
       a markdown list of links to local files at the very end of your response.
+    welcome_message: Ask me anything about Blorks.
     toolsets:
       - type: rag
         ref: blork_knowledge_base