[ROCm] [CI] Optimize Dockerfilerocm and reduce build time on CI (#885)

Signed-off-by: tjtanaa <tunjian.tan@embeddedllm.com>

docs/getting_started/quickstart.md

@@ -17,7 +17,13 @@ For installation on GPU from source:
 ```bash
 uv venv --python 3.12 --seed
 source .venv/bin/activate
+
+# On CUDA
 uv pip install vllm==0.14.0 --torch-backend=auto
+
+# On ROCm
+uv pip install vllm==0.14.0 --extra-index-url https://wheels.vllm.ai/rocm/0.14.0/rocm700
+
 git clone https://github.com/vllm-project/vllm-omni.git
 cd vllm-omni
 uv pip install -e .