Update readme

Signed-off-by: junjie.jiang <junjie.jiang@zilliz.com>

README.md

@@ -1,2 +1,51 @@
 # question-answer
 
+<br />
+
+
+
+## Desription
+
+Prompt to answer a question.
+
+
+<br />
+
+
+
+## Code Example
+
+### Example
+
+
+```python
+
+from towhee import ops, pipe
+import requests
+
+towhee_docs = requests.get('https://raw.githubusercontent.com/towhee-io/towhee/main/README.md').context
+
+
+p = (
+    pipe.input('question', 'docs', 'history')
+    .map(('question', 'docs', 'history'), 'prompt', ops.prompt.question_answer())
+    .map('prompt', 'answer', ops.LLM.OpenAI())
+    .output('answer')
+)
+
+an1 = p('Tell me something about Towhee', [towhee_docs], []).get()[0]
+
+an2 = p('Give an example', [towhee_docs], [{'question': 'Tell me something about Towhee', 'answer': an1}]).get()[0]
+
+```
+
+## Factory Constructor
+
+Create the operator via the following factory method:
+
+***ops.prompt.question_answer()***
+
+<br />
+
+
+**Returns:** *List[Dict]*