José Ralat has a job title that might leave some foodies with envy. Ralat travels around the U.S. and Mexico to eat, taste, and write about tacos. He is the Taco Editor at Texas Monthly Magazine and consequently the only taco editor in the United States. But, when we think of tacos, most of us think of them as Mexican food. In his new book, “American Tacos: A History and Guide,” Ralat dives into the evolution of tacos in the U.S. and its history in the borderlands.