V-slot naming inside DOM template fails with camelCase

[ReyFelipe]

The fix for this issue is in the pull request: #1679

Fix details

Modified the slot names from camelCase to kebab-case due the browser behaviour when you write the template directly inside the DOM. V-slot name is an attribute and the browser normalises that to all-lowercase.

Also modified the README.md to display kebab-case instead of camelCase.

While using this library with some colleagues, we ran into this issue and we think that the requested solution is the best fix. Would be greatly appreciated if you could accept so we can continue using the library.