Template Readmes and Standardization (#12819)

Co-authored-by: Erick Friis <erick@langchain.dev>

templates/xml-agent/README.md

@@ -31,7 +31,7 @@ langchain app add xml-agent
 
 And add the following code to your `server.py` file:
 ```python
-from xml_agent import chain as xml_agent_chain
+from xml_agent import agent_executor as xml_agent_chain
 
 add_routes(app, xml_agent_chain, path="/xml-agent")
 ```