README: No need to install package with tox
README: No need to install package with tox

Updates instructions to reflect this.

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