i've actually seen that before but the problem is i can only seem to find it dislocated, like in the link you just gave (thankyou btw). i can't seem to find a larger over all source that its from.
Ah, I thought they are always standalone docs like that? I don't think they're officially bundled into a unified source document.
You've likely seen this, too, but here's the page that links to the pdf to put it in "context" on the wotc site (no additional info, though): Warlock and Wizard | Dungeons & Dragons
I may be mistaken, though, as I'm still newish to 5e.
Anyway, hopefully someone else can chime in with a bit more info, happy hunting!