Here is the template:
It's not very good, and not really helpful, but it's so easy to make, you don't really even need the template! Just take your post-it pad and lay it on the bottom of your cardstock. The width is cut to the same width as the post-its. You will make four folds (crease well) and cut the front (top) corners however you like. Now you have your template. Cut out another piece without folding. Go ahead and decorate it/stamp with your design. Tape the post-it pad to the template at the very bottom with the sticky part of the post-its at the top. Fold it up and crease, embellish, and put a small piece of velcro on the bottom underside of the top flap to open and close.
Try it. It's a cute gift, and it's not near as hard to make as I made it sound:)