docs: use new nuxi module add command in installation (#471)

Author: danielroe

README.md

@@ -26,7 +26,7 @@
 1. Add `@nuxtjs/html-validator` as a dev dependency to your project
 
 ```bash
-yarn add @nuxtjs/html-validator --dev # or npm install @nuxtjs/html-validator --save-dev
+npx nuxi@latest module add html-validator
 ```
 
 2. Add `@nuxtjs/html-validator` to the `modules` section of `nuxt.config.ts`

docs/content/0.index.md

@@ -21,18 +21,9 @@ This module configures [`html-validate`](https://html-validate.org/) to automati
 ## Quick start
 
 ### Install
-
-::code-group
- ```bash [pnpm]
-  pnpm i -D @nuxtjs/html-validator
-  ```
- ```bash [Yarn]
-  yarn add @nuxtjs/html-validator --dev
-  ```
- ```bash [npm]
-  npm install @nuxtjs/html-validator --save-dev
-  ```
-::
+```bash
+npx nuxi@latest module add html-validator
+```
 
 ### nuxt.config.js