Doc: NuxtImg multiple formats

[Yves852]

Tested the format prop like the following, switching order and testing with typos. Image type (not extension) seems to change/fallback accordingly.

<NuxtImg format="webp,jpg" src="/nuxt-icon.png" ... />

Could the use of multiple format be explained in the doc for NuxtImg?

Is it advised to use multiple formats with NuxtImg comparing to NuxtPicture? If not could it have a warn in the doc against this practice?

Current doc: https://image.nuxt.com/usage/nuxt-img#format

Thanks.