It seems to me that the current set up excludes the vast majority of people (who are unlikely to know markdown, Git, or Github) which limits its effectiveness.
Maybe a good add-on project for someone is creating a website where potential new incidents can be submitted and evaluated, then pulled into the repo automatically if they pass muster.
Git's UI will absolutely limit the contributing audience, I agree - Perhaps the author could add a simple form for people to submit through and then technical people could manually add them? Google Form/Jotform/Survey Monkey style?
And this one is a general one about America's shit: https://github.com/mikeizbicki/american-shit (disclaimer: it's my repo)