added usage instructions for script family-html-snippet
added usage instructions for script family-html-snippet

graphicore/fontbakery,graphicore/fontbakery,moyogo/fontbakery,googlefonts/fontbakery,moyogo/fontbakery,googlefonts/fontbakery,graphicore/fontbakery,googlefonts/fontbakery,moyogo/fontbakery