docs: improve icons installations with all package managers

docs/content/1.getting-started/3.theming.md

@@ -117,10 +117,22 @@ Unlike the official [nuxt-icon](https://github.com/nuxt-modules/icon/) module, t
 
 However, you will need to install the icon packages you want to use.
 
-```sh
-yarn add --dev @iconify/json-{collection_name}
+::code-group
+
+```bash [yarn]
+yarn add -D @iconify/json-{collection_name}
+```
+
+```bash [npm]
+npm install -D @iconify/json-{collection_name}
 ```
 
+```sh [pnpm]
+pnpm i -D @iconify/json-{collection_name}
+```
+
+::
+
 You can easily replace all the default icons of the components in your `app.config.ts`.
 
 ```ts [app.config.ts]