Well, they gave a whole list of examples of how you might contribute to the "diversity" of their program (like special talents, unique service experiences, community involvement, etc.), so I picked out several things about myself or things that I've done that fall into some of those categories and wrote about how each made me more "diverse" (in a broad sense of the word). 6,000 characters is quite a bit, so there's plenty of room to talk about a variety of things.