Helping with python3 development

[Matthew Peveler]

Hello,

I was looking at Lilypond the other day wondering how I might give back to
this piece of software and noticed that it was still Python 2 and that Knut
Petersen made an invitation for help (
https://lists.gnu.org/archive/html/bug-lilypond/2019-08/msg00014.html). I'd
like to attempt to contribute to this effort in some part, though would
require some guidance on this front on how to contribute, especially given
that patches would be to a branch and not master, not fixing open bugs, etc.

Regards,
Matthew Peveler