docs: improve description for the webpack externals config in build script
docs: improve description for the webpack externals config in build script

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