Update docs with new total running requests metric

Author: BenjaminBraunDev

docs/proposals/003-model-server-protocol/README.md

@@ -28,6 +28,7 @@ effort.
 | Metric | Type | Description | vLLM metric | Triton TensorRT-LLM| SGLang |
 | ----- | ---- | ------------ | ---- | ---- | ---- |
 | TotalQueuedRequests         | Gauge     | The current total number of requests in the queue.| `vllm:num_requests_waiting`| `nv_trt_llm_request_metrics{request_type=waiting}`| `sglang:num_queue_reqs`
+| TotalRunningRequests         | Gauge     | The current total number of requests actively being served on the model server.| `vllm:num_requests_running`| `nv_trt_llm_request_metrics{request_type=scheduled}`| `sglang:num_running_reqs`
 | KVCacheUtilization| Gauge     | The current KV cache utilization in percentage.| `vllm:gpu_cache_usage_perc`| `nv_trt_llm_kv_cache_block_metrics{kv_cache_block_type=fraction}`| `sglang:token_usage`
 | [Optional] BlockSize         | Labeled     | The block size in tokens to allocate memory, used by the prefix cache scorer. If this metric is not available, the BlockSize will be derived from the [prefix plugin config](https://gateway-api-inference-extension.sigs.k8s.io/guides/epp-configuration/prefix-aware/#customize-the-prefix-cache-plugin).| name: `vllm:cache_config_info`, label name: `block_size`| | 
 | [Optional] NumGPUBlocks| Labeled     | The total number of blocks in the HBM KV cache, used by the prefix cache scorer. If this metric is not available, the NumGPUBlocks will be derived from the [prefix plugin config](https://gateway-api-inference-extension.sigs.k8s.io/guides/epp-configuration/prefix-aware/#customize-the-prefix-cache-plugin).| name: `vllm:cache_config_info`, label name: `num_gpu_blocks`| |