Update DocIndexRetriever Example to allow user passing in retriever/reranker params (#880)

Signed-off-by: minmin-intel <minmin.hou@intel.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

DocIndexRetriever/docker_compose/intel/cpu/xeon/README.md

@@ -79,13 +79,26 @@ Retrieval from KnowledgeBase
 
 ```bash
 curl http://${host_ip}:8889/v1/retrievaltool -X POST -H "Content-Type: application/json" -d '{
-     "text": "Explain the OPEA project?"
+     "messages": "Explain the OPEA project?"
      }'
 
 # expected output
 {"id":"354e62c703caac8c547b3061433ec5e8","reranked_docs":[{"id":"06d5a5cefc06cf9a9e0b5fa74a9f233c","text":"Close SearchsearchMenu WikiNewsCommunity Daysx-twitter linkedin github searchStreamlining implementation of enterprise-grade Generative AIEfficiently integrate secure, performant, and cost-effective Generative AI workflows into business value.TODAYOPEA..."}],"initial_query":"Explain the OPEA project?"}
 ```
 
+**Note**: `messages` is the required field. You can also pass in parameters for the retriever and reranker in the request. The parameters that can changed are listed below.
+
+    1. retriever
+    * search_type: str = "similarity"
+    * k: int = 4
+    * distance_threshold: Optional[float] = None
+    * fetch_k: int = 20
+    * lambda_mult: float = 0.5
+    * score_threshold: float = 0.2
+
+    2. reranker
+    * top_n: int = 1
+
 ## 5. Trouble shooting
 
 1. check all containers are alive