docs: dynamo-run clarify engine list (#522)

launch/dynamo-run/src/main.rs

@@ -32,7 +32,7 @@ Example:
 
 const ZMQ_SOCKET_PREFIX: &str = "dyn";
 
-const USAGE: &str = "USAGE: dynamo-run in=[http|text|dyn://<path>|batch:<folder>|none] out=[mistralrs|sglang|llamacpp|vllm|trtllm|echo_full|echo_core|pystr:<engine.py>|pytok:<engine.py>] [--http-port 8080] [--model-path <path>] [--model-name <served-model-name>] [--model-config <hf-repo>] [--tensor-parallel-size=1] [--num-nodes=1] [--node-rank=0] [--leader-addr=127.0.0.1:9876] [--base-gpu-id=0] [--extra-engine-args=args.json]";
+const USAGE: &str = "USAGE: dynamo-run in=[http|text|dyn://<path>|batch:<folder>|none] out=[See available engines below] [--http-port 8080] [--model-path <path>] [--model-name <served-model-name>] [--model-config <hf-repo>] [--tensor-parallel-size=1] [--num-nodes=1] [--node-rank=0] [--leader-addr=127.0.0.1:9876] [--base-gpu-id=0] [--extra-engine-args=args.json]";
 
 fn main() -> anyhow::Result<()> {
     logging::init();