I would say to just keep it short and sweet. Don't go into great detail about either incident. I also wrote a disciplinary addendum and I basically glossed over the facts, the punishment, and that I had learned an important lesson. In all reality, I highly doubt that admissions people are going to care too much about minor infractions a few years ago. Just write it to make the point that you are telling the truth and not hiding anything, and don't worry about it too much.