Point users towards useSortable in vueuse

[danvk]

I was struggling with some state synchronization issues with sortablejs-vue3 until I ran across this comment: https://github.com/MaxLeiter/sortablejs-vue3/issues/23#issuecomment-1496811292

It didn't solve my issue, but it did tell me that there's a useSortable in @vueuse. Switching to that fixed this issue and a few others, too. If this repo isn't actively maintained, it might benefit other developers to put a link to useSortable in the README.

https://vueuse.org/integrations/useSortable/#usesortable