### What this PR does / why we need it? Add LoRA user guide to DOC. The content refers to [LoRA Adapters](https://docs.vllm.ai/en/latest/features/lora.html). ### Does this PR introduce _any_ user-facing change? No ### How was this patch tested? No --------- Signed-off-by: paulyu12 <507435917@qq.com>