[DOC] Qwen3 PD disaggregation user guide (#2751)

### What this PR does / why we need it?
The PR is for the document of the prefiller&decoder disaggregation
deloyment guide.

The scenario of the guide is:
- Use 3 nodes totally and 2 NPUs on each node
- Qwen3-30B-A3B
- 1P2D
- Expert Parallel

The deployment can be used to verify PD Disggregation / Expert Parallel
features with a slightly less resources.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
No.


- vLLM version: v0.10.1.1
- vLLM main:
e599e2c65e

---------

Signed-off-by: paulyu12 <507435917@qq.com>

docs/source/tutorials/index.md

@@ -15,4 +15,5 @@ multi_npu_quantization
 single_node_300i
 multi_node
 multi_node_kimi
+multi_node_pd_disaggregation
 :::