[Docs] Add RL documentation (#17663)

Co-authored-by: JD <jaedon.guo@gmail.com>

docs/index.rst

@@ -16,6 +16,7 @@ Its core features include:
 - **Broad Model Support**: Supports a wide range of language models (Llama, Qwen, DeepSeek, Kimi, GLM, GPT, Gemma, Mistral, etc.), embedding models (e5-mistral, gte, mcdse), reward models (Skywork), and diffusion models (WAN, Qwen-Image), with easy extensibility for adding new models. Compatible with most Hugging Face models and OpenAI APIs.
 - **Extensive Hardware Support**: Runs on NVIDIA GPUs (GB200/B300/H100/A100/Spark), AMD GPUs (MI355/MI300), Intel Xeon CPUs, Google TPUs, Ascend NPUs, and more.
 - **Active Community**: SGLang is open-source and supported by a vibrant community with widespread industry adoption, powering over 400,000 GPUs worldwide.
+- **RL & Post-Training Backbone**: SGLang is a proven rollout backend across the world, with native RL integrations and adoption by well-known post-training frameworks such as AReaL, Miles, slime, Tunix, verl and more.
 
 .. toctree::
    :maxdepth: 1
@@ -63,6 +64,7 @@ Its core features include:
    advanced_features/deterministic_inference.md
    advanced_features/observability.md
    advanced_features/checkpoint_engine.md
+   advanced_features/sglang_for_rl.md
 
 .. toctree::
    :maxdepth: 1