DocDown still requires you to provide it with Pandoc, a Zotero .bib file, a CSL file, and a reference docx. Instructions for obtaining all of these are on the original blog post (follow steps 1-10 of the Referencing section and steps 1-4 of the Exporting section - DocDown will handle the rest.)
To make your life easier, the app comes bundled with CSL files for a couple of commonly used citation formats and a couple of basic Word templates I put together - all you need if you use these is your own .bib file.
Note: I don't have an Apple Developer certificate (£79 a year!), so when you first launch DocDown, it will warn you that it's from an unidentified developer. I am the developer, I have identified myself, do not fear. Follow these instructions to open the app - basically, right-click on the app icon and click 'Open' instead of double-clicking.
Enjoy, and let me know on GitHub or by email when you inevitably encounter problems! If anyone would like to help out with the source code on GitHub, your assistance will be warmly welcomed.