document usage of test_all_gfonts.sh & fb_summary_report.py
document usage of test_all_gfonts.sh & fb_summary_report.py

(issue #1056)

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