Based on the Papirus icon theme, available here: https://github.com/PapirusDevelopmentTeam/papirus-icon-theme.
Juice contains stock icons from the Papirus icon theme with modifications and new icons where needed. Available for download in your favorite iOS package manager at https://repo.hunterwittenborn.me.
Go to the issue page and create an issue with the Icon Requests template. One icon per issue, search issues before making a new one.
Look at CONTRIBUTE.md