Here's the article as written. It also has pictures with the zipper pinned in place before sewing it on.
Zippers can easily be added to a knit garment. Different weights of garments need different weight zippers. Heavy separating zippers are used on jackets and cardigans, while regular dressmaking zippers are used for neck or skirt openings. The zipper should be sewn in by hand using a backstitch through both the zipper and knit piece. To add a zipper, place the knit edges over the zipper so the zipper teeth are covered and the seam is centered over the zipper. From the right side , pin in place. On the wrong side tack the edges of the zipper to the garment. Turn to the right side and backstitch the zipper in place.
My thoughts on it: Sounds like you just sew it on where it looks good. But not with the sewing machine since it may bunch or get out of line. So whip your needle and thread out and go for it.