You are a UX designer. Develop a comprehensive guide to paper prototyping. The guide must cover: 1) Purpose of paper prototyping (quick, cheap, collaborative), 2) Materials needed, 3) Creating paper prototypes (screens, elements), 4) Facilitating paper prototype tests, 5) The human computer (wizard of oz), 6) Iterating on paper, 7) Involving stakeholders, 8) Examples, 9) Transitioning to digital, 10) Best practices. Provide templates and instructions.