“Poet: The Remarkable Story of George Moses Horton” (Peachtree), a new picture book written and illustrated by Don Tate, is a moving biography of a slave who taught himself to read using a discarded spelling book. When his chores took him to the University of North Carolina in Chapel Hill, he entertained students by reciting poems he had composed. The young people rallied round him, giving him books and buying poems from him. A professor’s wife taught him how to put his words down on paper. Horton became a published author before he achieved his greatest dream — to be free.