[DOC] add LoRA user guide (#1265)

### 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>

Author: paulyu12

docs/source/index.md

@@ -49,6 +49,7 @@ user_guide/env_vars
 user_guide/additional_config
 user_guide/sleep_mode
 user_guide/graph_mode.md
+user_guide/lora.md
 user_guide/quantization.md
 user_guide/release_notes
 user_guide/structured_output

docs/source/user_guide/lora.md

@@ -0,0 +1,8 @@
+# LoRA Adapters
+
+Like vLLM, vllm-scend supports LoRA as well. The usage and more details can be found in [vLLM official document](https://docs.vllm.ai/en/latest/features/lora.html).
+
+You can also refer to [this](https://docs.vllm.ai/en/latest/models/supported_models.html#list-of-text-only-language-models) to find which models support LoRA in vLLM.
+
+## Tips
+If you fail to run vllm-ascend with LoRA, you may follow [this instruction](https://vllm-ascend.readthedocs.io/en/latest/user_guide/graph_mode.html#fallback-to-eager-mode) to disable graph mode and try again.