Article day and I found a very descriptive article on N. graffami. This paper came out in June of 2009 describing the newly discovered Therizinosaurid and discussing the interesting new role of this herbivorous Theropod in the mix of what was once considered an entirely predatory line of dinosaur families. Also, there is this handout from the previously mentioned Arizona Museum of Natural History display on Nothronychus.
Therizinosaurs, like many other Cretaceous North American dinosaurs, share ancestry with other families of dinosaurs in Asian soil. If one were to trace the coelurosaur lineage back we could find that therizinosaurs, tyrannosaurs, dromaeosaurs, aves, troodontids, and ornithomimids are all related to a common ancestor. Ornithomimids have been questioned as omnivorous in the past eating plant and small animal/insect matter, however, Therizinosaurs are the first (to my knowledge at least) coelurosaurs to be assumed to be entirely herbivorous. The June 2009 article addresses this interesting twist in theropod evolution in a scientific manner and is worth listening to the arguments of it.