document status of the MScore font, update authors list etc.

document status of the MScore font, update authors list etc.

I’m currently attempting to get MScore relicenced to OFL-1.1
by explicit agreement from all co-authors:
https://gist.github.com/mirabilos/cc7b9a4d28d897ce1a4eba8a909e084e

*All* co-authors are informed about the situation and this plan.

I’ve collected enough agreements already and, with (at least)
concludent acting by MuseScore BVBA, feel comfortable enough
to continue distributing it like this, within Debian and without.

(also version the font properly and regenerate the .ttf file)