【main】[Doc]add 2P1D instruction for single node (#4716)

### What this PR does / why we need it?
Add the description for 2P1D， keeping it consistent with the content in
the dev branch.

### Does this PR introduce _any_ user-facing change?
no


- vLLM version: v0.12.0
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.12.0

Signed-off-by: mazhixin000 <mazhixinkorea@163.com>
Co-authored-by: wangxiyuan <wangxiyuan1007@gmail.com>

docs/source/tutorials/single_node_pd_disaggregation_llmdatadist.md

@@ -45,7 +45,7 @@ bash gen_ranktable.sh --ips 192.0.0.1 \
   --npus-per-node  2 --network-card-name eth0 --prefill-device-cnt 1 --decode-device-cnt 1
 ```
 
-The rank table will be generated at /vllm-workspace/vllm-ascend/examples/disaggregate_prefill_v1/ranktable.json
+If you want to run "2P1D", please set npus-per-node to 3 and prefill-device-cnt to 2. The rank table will be generated at /vllm-workspace/vllm-ascend/examples/disaggregate_prefill_v1/ranktable.json
 
 |Parameter  | Meaning |
 | --- | --- |
@@ -137,6 +137,8 @@ vllm serve /model/Qwen2.5-VL-7B-Instruct  \
 
 :::::
 
+If you want to run "2P1D", please set ASCEND_RT_VISIBLE_DEVICES, VLLM_ASCEND_LLMDD_RPC_PORT and port to different values for each P process.
+
 ## Example Proxy for Deployment
 
 Run a proxy server on the same node with the prefiller service instance. You can get the proxy program in the repository's examples: [load\_balance\_proxy\_server\_example.py](https://github.com/vllm-project/vllm-ascend/blob/main/examples/disaggregated_prefill_v1/load_balance_proxy_server_example.py)
@@ -151,6 +153,12 @@ python load_balance_proxy_server_example.py \
     --decoder-ports 13701
 ```
 
+|Parameter  | Meaning |
+| --- | --- |
+| --port | Port of proxy |
+| --prefiller-port | All ports of prefill |
+| --decoder-ports | All ports of decoder |
+
 ## Verification
 
 Check service health using the proxy server endpoint.