First add Zarginator to your build.zig.zon dependencies:
zig fetch --save git+https://github.com/Dan149/zarginator/#HEAD
Then add the dependency to your build.zig file:
(...)
const zarginator_package = b.dependency("zarginator", .{
.target = target,
.optimize = optimize,
});
const zarginator_module = zarginator_package.module("zarginator");
exe.root_module.addImport("zarginator", zarginator_module);
Import: const zarg = @import("zarginator");