Improve documentation on densities prop usage

[pascalwengerter]

From reading https://image.nuxt.com/usage/nuxt-img#densities, it's not clear to me how to provide the assets in a way that NuxtImg can handle them.

The provided codesnippet:

<NuxtImg
  src="/logos/nuxt.png"
  height="50"
  densities="x1 x2"
/>
<!--
<img
  src="/_ipx/w_50/logos/nuxt.png" 
  srcset="/_ipx/w_100/logos/nuxt.png x2"
/>
-->

implies that there is something happening in the background, taking the height of 50 times 1x/2x and adding a w_ prefix for the resource URL?

Ideally, I'd wish for some more examples and/or an explanation on what to expect - my use case is providing images from the public folder.