Side question: How did the author create the PDF from the markdown source at https://github.com/nh2/strace-pipes-presentation/blob/master... ?
Not with strace, that's for sure.
He used a tool called Marp [1].
At the top of the Markdown file you can see a code that reads "page_number: true" which can be found in the sample file provided by Marp here [2]. There are other tools out there that can be used to convert a Markdown into slides or PDF. I personally use Deckset.app [3] but searching "markdown presentation" — or — "markdown slides" on the Internet seems to bring a long list of projects aiming for the same feature set.
[1] https://yhatt.github.io/marp/
[2] https://raw.githubusercontent.com/yhatt/marp/master/example....
For example Pandoc which I personally enjoy