Documentation improvment - Add Apline.js x-data mention into modal

[marek5816]

According to this issue - wireui/wireui#981, multiple people have problem knowing that you need to set x-data scope for modal, because it depends on that.

Fro my my testing, any other components does not need this declaration, so this can be source of confusion.

Solution

Add some <x-alert title="Information!"> that will mention this x-data need