[Feature] Add custom fonts

[raphaelguimaraeszup]

Hi HarveyD, I'm doing a design system following your article (very thanks for this!) and now I need to add some custom fonts to my components, but it can also be in createGlobalStyle with styled-components , so I would like to propose this feature in your repo.

In case, I'm having trouble doing this on mine, if you've already seen this and know how to do it, if you can help me, I'd be very grateful.