Consider using Guiders-JS to document the UI

[felipesanches]

A very old issue on the fontbakery repo suggested using Guiders-JS to document the user interface:

https://github.com/pickhardt/Guiders-JS

I consider this to be an extremely low priority issue in the "maybe-someday" category. I'm just filling this here because the corresponding issue on the original issue tracker (fonttools/fontbakery#23) does not apply anymore to that repo, which is now focused on FontBakery-core only.