Patriots tight end Rob Gronkowski kicked off his book tour — yes, Gronk has written a book! — at the Barnes & Noble at the Pru on Thursday, but he had nothing to say about the arrests of former Pats tight end Aaron Hernandez or cornerback Alfonzo Dennard. (See story in Sports.) In addition to the book, titled “Growing Up Gronk: A Family’s Story of Raising Champions,” the hard-partying player this week launched the Gronk Nation Youth Foundation with a tailgate-themed bash at the Wellesley digs of Dan and Penny Fireman. The party produced by Altus Marketing and Management featured the five Gronkowski brothers — Rob, Gordie Jr., Chris, Glenn, and Dan — and their parents, and benefited the Brockton Junior Boxers, a Pop Warner football program that supports more than 250 kids.