Update README

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

README.md

@@ -34,6 +34,41 @@ messages=[
 answer = p(messages).get()[0]
 ```
 
+*Write a [retrieval-augmented generation pipeline](https://towhee.io/tasks/detail/pipeline/retrieval-augmented-generation) with explicit inputs/outputs name specifications:*
+
+```python
+from towhee import pipe, ops
+
+
+temp = '''Use the following pieces of context to answer the question at the end.
+If you don't know the answer, just say that you don't know, don't try to make up an answer.
+
+{context}
+
+Question: {question}
+
+Helpful Answer:
+'''
+
+
+docs = ['You can install towhee via command `pip install towhee`.']
+history = [
+    ('What is Towhee?', 'Towhee is an open-source machine learning pipeline that helps you encode your unstructured data into embeddings.')
+]
+question = 'How to install it?'
+
+p = (
+    pipe.input('question', 'docs', 'history')
+        .map(('question', 'docs', 'history'), 'prompt', ops.prompt.template(temp, ['question', 'context']))
+        .map('prompt', 'answer',
+             ops.LLM.OpenAI(api_key=OPENAI_API_KEY, temperature=0.5, max_tokens=100)
+             )
+        .output('answer')
+)
+
+answer = p(question, docs, history).get()[0]
+```
+
 <br />
 
 ## Factory Constructor