Followed the readme steps, and tried installing from the latest release .zip, but was unsuccessful. Also tried opening things in a different order just in case (opening Xcode first then Uncrustifier, opening Uncrustifier first then Xcode, opening Uncrustifier with project open and without a project open). Still seems unsuccessful (doesn't show up in my Editor menu). Deleted all old Xcode plugins in ~/Library/Application\ Support/Developer/Shared/Xcode just in case it was interfering in some way. Still unsuccessful.
Looking at Activity Monitor does not show 'Uncrustify' running as it would be during a successful installation on Xcode launch.
Running macOS 10.11.6
Xcode 8.0