docs: add object syntax for event handler

docs/content/1.guide/3.routing.md

@@ -221,6 +221,8 @@ export default defineEventHandler((event) => {
 })
 ```
 
+Middleware in `middleware/` directory are automatically registered for all routes. If you want to register a middleware for a specific route, see [Object Syntax Event Handler](#object-syntax-event-handler).
+
 ::alert
 Returning anything from a middleware will close the request and should be avoided! Any returned value from middleware will be the response and further code will not be executed however **this is not recommended to do!**
 ::
@@ -261,3 +263,39 @@ export default defineEventHandler((event) => {
   }
 })
 ```
+
+## Object Syntax Event Handler
+
+Since H3@1.8, you can use a new object syntax to define event handler.
+
+::alert{type=primary}
+Read the announcement on the [UnJS blog](https://unjs.io/blog/2023-08-15-h3-towards-the-edge-of-the-web#object-syntax-event-handlers).
+::
+
+You can start by defining middleware in a file like `utils/auth.ts` to be able to auto-import them in your routes:
+
+```ts [utils/auth.ts]
+export const auth = defineRequestMiddleware((event) => {
+  event.context.auth = { name: 'admin' }
+})
+```
+
+```ts [utils/log.ts]
+export const log = defineRequestMiddleware((event) => {
+  console.log(event)
+})
+```
+
+Then, you can use them in your routes:
+
+```ts [routes/hello.ts]
+export default eventHandler({
+  onRequest: [auth],
+  onBeforeResponse: [log],
+  async handler(event) {
+    return `Hello ${event.context.auth?.name || 'Guest'}`
+  },
+})
+```
+
+This synxtax allows you to order and define middleware before the handler and before the response.