MAINTAINERS: Add myself as Darwin maintainer
I do some development and usage of FFmpeg regularly on macOS and sent
some patches to fix issues specific to Darwin in the past so I think it
makes sense to add myself as maintainer so people know they can ping me
if required, for Darwin specific issues/testing.
I have both Intel and Apple Silicon (aarch64) machines as well as older
Macs for testing on older macOS versions if necessary.
Marvin Scholz