Mac Install MuseScore default path

[djaychela]

The default path for MuseScore on macOS is:

environment.set('musicxmlPath', '/Applications/MuseScore 3.app/Contents/MacOS/mscore')

[djaychela]

The first time you run it from this, MuseScore will run through a set of defaults to be set, but will still open up the score that has been sent to it (which is nice!)

[geokala]

Do you think that supporting documentation would need to mention MuseScore giving the popups on first run?

(probably respond on #13 if you get a chance)