[Doc] Update CPU doc (#20676)

Signed-off-by: jiang1.li <jiang1.li@intel.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/getting_started/installation/cpu/s390x.inc.md

@@ -61,6 +61,23 @@ Execute the following commands to build and install vLLM from the source.
 # --8<-- [end:pre-built-images]
 # --8<-- [start:build-image-from-source]
 
+```bash
+docker build -f docker/Dockerfile.s390x \
+        --tag vllm-cpu-env .
+
+# Launching OpenAI server
+docker run --rm \
+            --privileged=true \
+            --shm-size=4g \
+            -p 8000:8000 \
+            -e VLLM_CPU_KVCACHE_SPACE=<KV cache space> \
+            -e VLLM_CPU_OMP_THREADS_BIND=<CPU cores for inference> \
+            vllm-cpu-env \
+            --model=meta-llama/Llama-3.2-1B-Instruct \
+            --dtype=float \
+            other vLLM OpenAI server arguments
+```
+
 # --8<-- [end:build-image-from-source]
 # --8<-- [start:extra-information]
 # --8<-- [end:extra-information]