New comment by CameronNemo on void-packages repository

https://github.com/void-linux/void-packages/pull/20735#issuecomment-616310296

Comment:
I guess optional dependencies could be documented there, but I am not sure how many people will look... `python3-matplotlib` and `scapy` both use INSTALL.msg files to suggest optional dependencies.

Likewise service configuration that is less-than-straightforward (e.g. mopidy, minio) seems like a good category of information to put in these README files.