Joy not only has written instructions, found here - Joyful Expressions - but she has also prepared a video tutorial on finishing the knit V-neck. I encourage you to watch it. You will notice that she is using her Sure-Fit Designs Dress Kit bodice for her pattern. (Joy has made so many SFD blouses and tops, that she has a body blueprint (personal sloper) for working with both wovens and knit fabrics. Also, you'll likely notice that she has moved the side bust dart down into the lower side seam.)
During this tutorial, she shows you how to draw/trace a facing for the neckline. In addition to her visual instructions, please realize that the written instructions for drawing a perfectly fitting facing are found on page 20 of the SFD Dress Kit Instruction Book.
This is a 2-Part Tutorial. Here's Part 1.