[INSTALL.md] modify ots-sanitize installation approach
[INSTALL.md] modify ots-sanitize installation approach

associated issue report https://github.com/googlefonts/fontbakery/issues/2041
graphicore/fontbakery,googlefonts/fontbakery,graphicore/fontbakery,moyogo/fontbakery,moyogo/fontbakery,googlefonts/fontbakery,googlefonts/fontbakery,graphicore/fontbakery,moyogo/fontbakery