[Doc ] Supplement kvpool user guide (#5013)

### What this PR does / why we need it?
Supplement detailed descriptions for `ASCEND_CONNECT_TIMEOUT` and
`ASCEND_TRANSFER_TIMEOUT` in kvpool.

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: LCAIZJ <leichao139636@163.com>

docs/source/user_guide/feature_guide/kv_pool.md

@@ -85,9 +85,16 @@ export PYTHONPATH=$PYTHONPATH:/xxxxx/vllm
 export MOONCAKE_CONFIG_PATH="/xxxxxx/mooncake.json"
 export ASCEND_RT_VISIBLE_DEVICES=0,1,2,3
 export ACL_OP_INIT_MODE=1
-export ASCEND_BUFFER_POOL=4:8
+
 # ASCEND_BUFFER_POOL is the environment variable for configuring the number and size of buffer on NPU Device for aggregation and KV transfer，the value 4:8 means we allocate 4 buffers of size 8MB.
+export ASCEND_BUFFER_POOL=4:8
+
+# Unit: ms. The timeout for one-sided communication connection establishment is set to 10 seconds by default (see PR: https://github.com/kvcache-ai/Mooncake/pull/1039). Users can adjust this value based on their specific setup.
+# The recommended formula is: ASCEND_CONNECT_TIMEOUT = connection_time_per_card (typically within 500ms) × total_number_of_Decode_cards.
+# This ensures that even in the worst-case scenario—where all Decode cards simultaneously attempt to connect to the same Prefill card the connection will not time out.
 export ASCEND_CONNECT_TIMEOUT=10000
+
+# Unit: ms. The timeout for one-sided communication transfer is set to 10 seconds by default (see PR: https://github.com/kvcache-ai/Mooncake/pull/1039).
 export ASCEND_TRANSFER_TIMEOUT=10000
 
 python3 -m vllm.entrypoints.openai.api_server \