Fix README: arguments are positional, not flags

README.md

@@ -12,7 +12,13 @@ A simple Rust application that publishes messages to an MQTT broker.
 ## Usage
 
 ```bash
-cargo run -- --broker 192.168.1.100 --port 1883
+cargo run -- 192.168.1.100 1883
+```
+
+Or run the binary directly:
+
+```bash
+./target/debug/mqtt-publisher [broker] [port]
 ```
 
 ### Arguments