docs: add tip openai page (#15866)

Co-authored-by: mubashir1osmani <[email protected]>

Author: mubashirosmani

docs/my-website/docs/providers/openai.md

@@ -4,6 +4,10 @@ import TabItem from '@theme/TabItem';
 # OpenAI
 LiteLLM supports OpenAI Chat + Embedding calls.
 
+:::tip
+**We recommend using `litellm.responses()` / Responses API** for the latest OpenAI models (GPT-5, gpt-5-codex, o3-mini, etc.)
+:::
+
 ### Required API Keys
 
 ```python