docs: add required radio & checkbox
docs: add required radio & checkbox

abdullahsalem/foundation-sites,zurb/foundation,zurb/foundation-sites,DaSchTour/foundation-sites,DaSchTour/foundation-sites,zurb/foundation-sites,zurb/foundation,zurb/foundation-sites,zurb/foundation,abdullahsalem/foundation-sites,abdullahsalem/foundation-sites