I finally got Pijul upgraded and running. I did this by following the journey described here: https://discourse.pijul.org/t/newbie-feedback/328

I found this upon googling the command line errors that I was encountering when running the commands mentioned in the Pijul manual. It's disheartening to see that the manual still hasn't been updated to reflect these needs despite that in the first link above that the original poster suggested that this manual be updated, and they posted this suggestion in April (2019), four-ish months ago. Thankfully, someone has contributed a patch that would improve the page! But it hasn't been merged/integrated into the repo yet, over two months later.