Add info in docs on how to use item-@ without causing invalid attribute error

[olemarius]

Just a quick suggestion that might help others, as it took some time to figure out..

<template #item-@="{ item }"> causes eslint error in a vue 3 + ts project

<template #[item-@]="{ item }"> works

[claide]

@olemarius tried it but I got Parsing error: Expression expected