Typefaces has been deprecated

This [page](https://gridsome.org/docs/assets-fonts/#self-hosting-open-source-typefaces) of documentation endorses the [Typefaces project](https://github.com/KyleAMathews/typefaces) which has been long deprecated in favour of [Fontsource](https://github.com/fontsource/fontsource).

The documentation should probably be updated as other major libraries like Gatsby and Material UI have replaced their references to Fontsource in theirs as well.

Start with the documentation page at gridsome.org/docs/assets-fonts/#self-hosting-open-source-typefaces and review its reference to the deprecated Typefaces project. Update the page to recommend Fontsource instead, then verify that the revised links and guidance are accurate.

Written by the indexing model from the issue text.