How to select an arbitrary MP3 as ringtone on LineageOS?

I encoded a part of a song as MP3 and I'd like to set it as ringtone on LineageOS 14. I found some instructions to move the file to a certain location - or better locations because the locations because they seem to differ based on model and version. However, it's 2018 and developers are usually educated in basic UX, so there's probably an acceptable way to do this (assuming that it's not acceptable to force a user to speculate that a configuration option might be available after moving a file to a certain unspecified location in the context of a GUI - [forum threads like this one of a German LineageOS forum not based on meritocratic swarm intelligence suggest five contradictory approaches](https://www.lineage-os-forum.de/Thread-CM-MP3-als-Klingelton)) . I'm using LineageOS 14.1 on a Moto G 2014.