Improve vLLM provider documentation

[terrytangyuan]

🚀 Describe the new functionality needed

https://llama-stack.readthedocs.io/en/latest/distributions/self_hosted_distro/remote-vllm.html

Provide a good quick-start command to start vLLM server and redirect specific instructions for different hardware to vLLM website (I believe there's an ongoing efforts to improve vLLM documentation).

💡 Why is this needed? What if we don't build it?

TBA

Other thoughts

No response