[docs] Show user the fastAPI docs available (#17510)

Signed-off-by: vincentzed <207368749+vincentzed@users.noreply.github.com>

docs/basic_usage/send_request.ipynb

@@ -5,7 +5,7 @@
    "metadata": {},
    "source": [
     "# Sending Requests\n",
-    "This notebook provides a quick-start guide to use SGLang in chat completions after installation.\n",
+    "This notebook provides a quick-start guide to use SGLang in chat completions after installation. Once your server is running, API documentation is available at `http://localhost:30000/docs` (Swagger UI), `http://localhost:30000/redoc` (ReDoc), or `http://localhost:30000/openapi.json` (OpenAPI spec, useful for AI agents). Replace `30000` with your port if using a different one.\n",
     "\n",
     "- For Vision Language Models, see [OpenAI APIs - Vision](openai_api_vision.ipynb).\n",
     "- For Embedding Models, see [OpenAI APIs - Embedding](openai_api_embeddings.ipynb) and [Encode (embedding model)](native_api.html#Encode-(embedding-model)).\n",