docs: incorrect method (#904)

docs/src/usage/arbiter_engine/agents_and_engines.md

@@ -46,7 +46,7 @@ use crate::Replier;
 fn setup() {
     let ping_replier = Replier::new("ping", "pong", 5, None);
     let pong_replier = Replier::new("pong", "ping", 5, Some("ping"));
-    let agent = Agent::new("my_agent")
+    let agent = Agent::builder("my_agent")
                     .with_behavior(ping_replier)
                     .with_behavior(pong_replier);
 }
@@ -55,4 +55,4 @@ In this example, we have created an `Agent` with two `Replier` behaviors.
 The `ping_replier` will reply to a message with "pong" and the `pong_replier` will reply to a message with "ping".
 Given that the `pong_replier` has a `startup_message` of "ping", it will send a message to everyone (including the "my_agent" itself who holds the `ping_replier` behavior) when it starts up.
 This will start a chain of messages that will continue in a "ping" "pong" fashion until the `max_count` is reached.
-```
+```