Add German language links to the translations page (#3157)

* Add German language links to the translations page
Co-authored-by: Jinjiang <[email protected]>

* Edit source link
Co-authored-by: Jinjiang <[email protected]>

Author: roma-marshall

src/translations/index.md

@@ -25,6 +25,7 @@ aside: false
 - [العربية / Arabic](https://ar.vuejs.org/) [[source](https://github.com/vuejs-translations/docs-ar)]
 
 - [Español / Spanish](https://vue3-spanish-docs.netlify.app/) [[source](https://github.com/icarusgk/vuejs-spanish-docs)]
+- [Deutsch / German](https://de-vue-docs.netlify.app/) [[source](https://github.com/vuejs-translations/docs-de)]
 
 ## Starting a new Translation {#starting-a-new-translation}