[Doc] Add vllm-metal to hardware plugin documentation (#31174)

Signed-off-by: mgoin <mgoin64@gmail.com>

docs/getting_started/installation/README.md

@@ -28,3 +28,4 @@ The backends below live **outside** the main `vllm` repository and follow the
 | Cambricon MLU | `vllm-mlu` | <https://github.com/Cambricon/vllm-mlu> |
 | Baidu Kunlun XPU | N/A, install from source | <https://github.com/baidu/vLLM-Kunlun> |
 | Sophgo TPU | N/A, install from source | <https://github.com/sophgo/vllm-tpu> |
+| Apple Silicon (Metal) | N/A, install from source | <https://github.com/vllm-project/vllm-metal> |

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

@@ -4,6 +4,9 @@ vLLM has experimental support for macOS with Apple Silicon. For now, users must
 
 Currently the CPU implementation for macOS supports FP32 and FP16 datatypes.
 
+!!! tip "GPU-Accelerated Inference with vLLM-Metal"
+    For GPU-accelerated inference on Apple Silicon using Metal, check out [vllm-metal](https://github.com/vllm-project/vllm-metal), a community-maintained hardware plugin that uses MLX as the compute backend.
+
 # --8<-- [end:installation]
 # --8<-- [start:requirements]