[Docs] Improve `priority` parameter documentation (#29572)

Signed-off-by: maang <maang_h@163.com>
Signed-off-by: maang-h <55082429+maang-h@users.noreply.github.com>
Co-authored-by: Cyrus Leung <cyrus.tl.leung@gmail.com>

vllm/entrypoints/llm.py

@@ -405,6 +405,9 @@ class LLM:
             lora_request: LoRA request to use for generation, if any.
             priority: The priority of the requests, if any.
                 Only applicable when priority scheduling policy is enabled.
+                If provided, must be a list of integers matching the length
+                of `prompts`, where each priority value corresponds to the prompt
+                at the same index.
 
         Returns:
             A list of `RequestOutput` objects containing the