docs(vue): add vue-router in installation sections

Related to #2764

README.md

@@ -74,11 +74,18 @@ export default defineConfig({
 
 ```ts [main.ts]
 import { createApp } from 'vue'
+import { createRouter, createWebHistory } from 'vue-router'
 import ui from '@nuxt/ui/vue-plugin'
 import App from './App.vue'
 
 const app = createApp(App)
 
+const router = createRouter({
+  routes: [],
+  history: createWebHistory()
+})
+
+app.use(router)
 app.use(ui)
 
 app.mount('#app')