[doc][misc] clarify VLLM_HOST_IP for multi-node inference (#12667)
As more and more people are trying deepseek models with multi-node
inference, https://github.com/vllm-project/vllm/issues/7815 becomes more
frequent. Let's give clear message to users.
Signed-off-by: youkaichao <youkaichao@gmail.com>
