Link the Figma Document/Design language/Design standards in more places in the contributor guide.

As Bevy UI gets more capable (thanks BSN & Feathers!) we should document standards for examples & the editor in more areas in the contribution guide.

Right now Figma is what the editor UI has been sketched out in, so it'd be a good candidate for a thing to link to for this.

Start by locating the contributor guide and review its sections covering examples, the editor, and UI standards. Add links to the Figma document, design language, or design standards where relevant; done means contributors can find the Figma-based guidance from the relevant guide sections.

Written by the indexing model from the issue text.