Add open file with the app.

[Stanlyhalo]

Obviously we can forcefully have our os (mine is windows) to open all .mtz files with Materialize... and it fits right in, however the app doesn't automatically load the project, idk if this can be done with Unity, I'm sure there's some way to do it but of course, if it can be done, no worries. Just a suggestion (suggesting here because the app suggestion box won't send).