Add warning: Vetur is for Vue 2.x and Volar for Vue 3.x

[JulioJu]

Hi,

Thanks for this project. But as we can see on Vetur page, it is outdated. See also vuejs/vetur#3476 .

Maybe on top of the README we could add a link to coc-volar . We could say that coc-vetur is for Vue.JS 2.x and Coc-Volar for Vue.JS 3.x

See also vuejs/language-tools#273 .

I was confused, and probably other developers are like me.

I could make a PR if you want.

What do you think about that ?

[fannheyward]

I could make a PR if you want

PR is welcome.