docs: add vuetify peer-dependency install step (#330, #378)

Author: AndreyYolkin

docs/guide/index.md

@@ -40,7 +40,29 @@ You can also try it online on StackBlitz:
 
 ### Existing Project
 
-If you already have a Nuxt project, you can add the module using `nuxt`:
+If you already have a Nuxt project, first install `vuetify` — it is a peer dependency, so you choose the major version (Vuetify 3 or 4):
+
+::: code-group
+
+```bash [npm]
+npm install -D vuetify
+```
+
+```bash [yarn]
+yarn add -D vuetify
+```
+
+```bash [pnpm]
+pnpm add -D vuetify
+```
+
+```bash [bun]
+bun add -D vuetify
+```
+
+:::
+
+Then add the module using `nuxt`:
 
 ::: code-group
 

packages/vuetify-nuxt-module/README.md

@@ -51,7 +51,10 @@
 
 > Requires Vite, will not work with Webpack
 
+`vuetify` is a peer dependency (Vuetify 3 or 4) — install it alongside the module:
+
 ```bash
+npm install -D vuetify
 npx nuxt module add vuetify-nuxt-module
 ```