Missing Docs regarding audio sample channel layout

[Green-Sky]

I spend quiet some time scouring through the wiki and headers, trying to figure out whether SDL interleaves channels or not. In the end I looked at the source and yes, it does. https://github.com/libsdl-org/SDL/blob/0df12d223c322a508aa72a781be4e80f58538f70/src/audio/SDL_audio_channel_converters.h#L36-L40

This should really be documented somewhere.