examples: update langchain-python-simple (#3591)

- better formatting of input prompt
- use invoke instead of predict

examples/langchain-python-simple/main.py

@@ -1,6 +1,6 @@
 from langchain.llms import Ollama
 
-input = input("What is your question?")
+input = input("What is your question?\n> ")
 llm = Ollama(model="llama3.2")
-res = llm.predict(input)
+res = llm.invoke(input)
 print (res)