[Docs] Update notebooks to use START (#902)

examples/chatbot-simulation-evaluation/simulation_utils.py

@@ -9,7 +9,7 @@ from langchain_core.runnables import chain as as_runnable
 from langchain_openai import ChatOpenAI
 from typing_extensions import TypedDict
 
-from langgraph.graph import END, StateGraph
+from langgraph.graph import END, StateGraph, START
 
 
 def langchain_to_openai_messages(messages: List[BaseMessage]):
@@ -116,7 +116,7 @@ def create_chat_simulator(
         should_continue or functools.partial(_should_continue, max_turns=max_turns),
     )
     # If your dataset has a 'leading question/input', then we route first to the assistant, otherwise, we let the user take the lead.
-    graph_builder.set_entry_point("assistant" if input_key is not None else "user")
+    graph_builder.add_edge(START, "assistant" if input_key is not None else "user")
 
     return (
         RunnableLambda(_prepare_example).bind(input_key=input_key)