docs: Add more clarification around Bird.stop()

closes: #3323

site/docs/00-tutorial/03-step-bird-and-ground.mdx

@@ -51,6 +51,14 @@ export class Bird extends ex.Actor {
     override onInitialize(): void {
         this.acc = ex.vec(0, 1200); // pixels per second per second
     }
+
+		start() {
+      // later we'll use this to start our bird after game over
+		}
+
+		stop() {
+      // later we'll use this to stop our bird after collision
+		}
 }
 ```
 

site/docs/00-tutorial/05-step-plumbing-pipes.mdx

@@ -39,6 +39,8 @@ export class Pipe extends ex.Actor {
 
 To make the `Bird` "collide" with our pipes we need to adjust our `onCollisionStart` to account for `Pipe`.
 
+We'll use the `stop()` method we created in step 3 to stop our bird from moving when we collide.
+
 ```typescript
 // bird.ts
 import * as ex from 'excalibur';