added another middleware example

middleware.ts

@@ -0,0 +1,24 @@
+import { Application, Context, Next, Router } from "jsr:@oak/oak";
+
+interface HelloWorldState {
+  hello?: string;
+  world?: string;
+}
+async function hello(ctx: Context<HelloWorldState>, next: Next) {
+  ctx.state.hello = "Hello";
+  await next();
+}
+async function world(ctx: Context<HelloWorldState>, next: Next) {
+  ctx.state.world = "world";
+  await next();
+}
+
+const router = new Router<HelloWorldState>();
+router.get("/hello", hello, world, (ctx) => {
+  ctx.response.body = `${ctx.state.hello}, ${ctx.state.world}!`;
+});
+
+const app = new Application<HelloWorldState>();
+app.use(router.routes());
+app.use(router.allowedMethods());
+app.listen({ port: 8000 });