docs: update plugin provide example (#5386)

docs/content/2.guide/3.directory-structure/11.plugins.md

@@ -47,7 +47,7 @@ If you would like to provide a helper on the `NuxtApp` instance, return it from
 export default defineNuxtPlugin(() => {
   return {
     provide: {
-      hello: () => 'world'
+      hello: (msg: string) => `Hello ${msg}!`
     }
   }
 })
@@ -58,7 +58,7 @@ In another file you can use this:
 ```vue
 <template>
   <div>
-    {{ $hello() }}
+    {{ $hello('world') }}
   </div>
 </template>