chore(readme): improve deploy button

Author: benjamincanac

README.md

@@ -23,7 +23,7 @@ npx nuxi init -t github:nuxt-ui-templates/docs
 
 ## Deploy your own
 
-[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/clone?repository-url=https%3A%2F%2Fgithub.com%2Fnuxt-ui-templates%2Fdocs)
+[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/clone?repository-url=https%3A%2F%2Fgithub.com%2Fnuxt-ui-templates%2Fdocs&demo-image=https%3A%2F%2Fui4.nuxt.com%2Fassets%2Ftemplates%2Fnuxt%2Fdocs-dark.png&demo-url=https%3A%2F%2Fdocs-template.nuxt.dev%2F&demo-title=Nuxt%20Docs%20Template&demo-description=A%20documentation%20template%20powered%20by%20Nuxt%20Content.)
 
 ## Setup