[css-font-loading] editorial: the definition of document.fonts is really hard to find

[MatsPalmgren]

https://drafts.csswg.org/css-font-loading/#font-face-source

It took me quite some time to find that this is the place where document.fonts is specified. I'd appreciate if this could be made clearer.

Suggestions:

• perhaps mention document.fonts right in the Introduction and link it to #font-face-source to make it clear that this is the specification that defines document.fonts
• change "The FontFaceSource mixin" chapter title to include "document.fonts"
• at a minimum, linkify the first occurrence of document.fonts

[tabatkins]

Good idea, done.