[Doc] Refactor the DeepSeek-V3.1 tutorial. (vllm-project#4399)

### What this PR does / why we need it?
Refactor the DeepSeek-V3.1 tutorial.

- vLLM version: v0.11.2
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

Signed-off-by: 1092626063 <[email protected]>
Signed-off-by: Che Ruan <[email protected]>

Author: 1092626063