Suggest users use sox to convert to wav on the README

[WillNilges]

It looks like you can use sox to convert files to wav for use with sampleZone.
To install on Debian: apt install sox and for mp3 support: apt install libsox-fmt-mp3

[WillNilges]

What if we just... Included sox functionality? When a file that was not .wav was opened with sampleZone, there'd be a way to either automatically or manually convert it.