mention restricted headers

[amesgen]

Motivated by this.

Editing this markdown file is a pain due to articifial line breaks, do we want to do something about it (-> long lines)?

[rossabaker]

I've started doing sentence-per-line in my Markdown. Word-wrap runs into the problem you mention, and long lines aren't great for diffs. Sentence-per-line is pleasing from a git perspective, but not so pleasing visually. I don't have a great answer here.