accessibility blurb for website

[Mark Polesky]

I propose to add this section on the Features page, just after
"Text-based input" (and before "Mix music and text").

- Mark


Accessibility

Text-based input also makes score-writing possible for users with
severe physical disabilities. Dexterity-impaired users who are
unable to type or control a computer mouse can use
speech-recognition software to edit LilyPond files. Even users who
are totally blind can use screen-reading software to navigate
their way through LilyPond files---an impossible task in
graphical-based score-writing programs.

p.s. "---" means em-dash, I guess. Alternatively you could
     parenthesize the last clause.