Add an example that demonstrates how to set the texture of 3D meshes from images

[alice-i-cecile]

How can Bevy's documentation be improved?

The existing texture example is very basic, and only shows how to set these up with simple colors.

We should demonstrate how to use custom images (and define a UV mapping). The 3D use of a TextureAtlas may also make sense in this example.

Prompted by this Discord help thread.