Readme Update

[nicholasoxford]

Update readme to work with newest version of vue 3

[frandiox]

@nicholasoxford Thanks for the PR!
I think the <script setup> syntax is still not really widespread in Vue community so I think the more traditional syntax (exporting a component with setup function) is actually a better fit for an example.
Most devs who know about the newest syntax should probably understand about the setup function anyway 🤔

I'm closing this for now but I'll check it if I change my mind 👍