Update example codes

Signed-off-by: Jael Gu <mengjia.gu@zilliz.com>

README.md

@@ -25,9 +25,13 @@ Use the default model to continue the conversation from given messages.
 ```python
 from towhee import ops
 
-chat = ops.LLM.Llama_2('llama-2-13b-chat', max_tokens=2048)
+chat = ops.LLM.Llama_2('llama-2-13b-chat', max_tokens=512)
 
-message = [{"question": "Building a website can be done in 10 simple steps:"}]
+message = [
+    {'system': 'You are a very helpful assistant.'},
+    {'question': 'Who won the world series in 2020?', 'answer': 'The Los Angeles Dodgers won the World Series in 2020.'},
+    {'question': 'Where was it played?'}
+]
 answer = chat(message)
 ```
 
@@ -39,13 +43,14 @@ from towhee import pipe, ops
 p = (
     pipe.input('question', 'docs', 'history')
         .map(('question', 'docs', 'history'), 'prompt', ops.prompt.question_answer())
-        .map('prompt', 'answer', ops.LLM.Llama_2('llama-2-7b-chat', stop='</s>'))
+        .map('prompt', 'answer', ops.LLM.Llama_2('llama-2-7b-chat'))
         .output('answer')
 )
 
-history=[('Who won the world series in 2020?', 'The Los Angeles Dodgers won the World Series in 2020.')]
-question = 'Where was it played?'
-answer = p(question, [], history).get()[0]
+history=[('What is Towhee?', 'Towhee is a cutting-edge framework designed to streamline the processing of unstructured data through the use of Large Language Model (LLM) based pipeline orchestration.')]
+knowledge = ['You can install towhee via `pip install towhee`.']
+question = 'How to install it?'
+answer = p(question, knowledge, history).get()[0]
 ```
 
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