PUT THIS one on your calendar and try to arrange for Dutton to invite you. Former Texas Gov. Ann Richards launches her latest book, "I'm Not Slowing Down," on Aug 12 at Jean-Luc Restaurant, 6 to 8 p.m. I liked the invitation which reads "Tex in the City and Jean-Luc invite . . ." This book is all about Ann's successful battle with osteoporosis, which is one of her great causes.