docs(plugins): usage with vue plugins (#1129)

Co-authored-by: pooya parsa <pyapar@gmail.com>

docs/content/3.docs/1.usage/4.nuxt-app.md

@@ -39,7 +39,7 @@ In Nuxt 2 plugins, this was referred to as [inject function](https://nuxtjs.org/
 
 ```js
 const nuxtApp = {
-  app, // the global Vue application: https://v3.vuejs.org/api/application-api.html
+  vueApp, // the global Vue application: https://v3.vuejs.org/api/application-api.html
 
   // These let you call and add runtime NuxtApp hooks
   // https://github.com/nuxt/framework/blob/main/packages/nuxt3/src/app/nuxt.ts#L18

docs/content/3.docs/2.directory-structure/10.plugins.md

@@ -41,3 +41,33 @@ declare module '#app' {
   }
 }
 ```
+
+## Vue plugins
+
+If you want to use Vue plugins, like [vue-gtag](https://github.com/MatteoGabriele/vue-gtag) to add Google analytics tags, you can use a nuxt plugin to do so.
+
+> There is an Open RFC to make this even easier! See [nuxt/framework#1175](https://github.com/nuxt/framework/discussions/1175)
+
+First install the plugin you want.
+
+```bash
+yarn add --dev vue-gtag
+```
+
+Then create a plugin file `plugins/vue-gtag.client.js`.
+
+```ts
+import { defineNuxtPlugin } from "#app";
+import VueGtag from "vue-gtag";
+
+export default defineNuxtPlugin((nuxtApp) => {
+  nuxtApp.vueApp.use(VueGtag, {
+    config: {
+      id: "GA_MEASUREMENT_ID",
+      params: {
+        anonymize_ip: true,
+      },
+    },
+  });
+});
+```