Presenter Notes
This is not a official part of markdown, but in terms of a slide presentation application, you really need presenter or speaker notes, so here's a way to do it:
;; I am a speaker note
As with quotes (above), you can add multiple lines of speaker notes, also just like with quotes, you need to keep an empty line before the next element begins:
;; I am the first line of speaker notes
;; I am the second line of speaker notes
I am a normal paragraph again