Just to clarify, I'm asking where to host a static page that would be a modified introduction, addendum, errata, "if you like this try these", "The author died by wooden badger attack", etc

Not the entire book. I wouldn't have to copyleft the entire thing, right?

My current static page is just an "I like this book, please give me this free thing and put me on a mailing list" kind of thing. But that's not really the point. The point is "how can I use static pages, presumably the thing the internet was built for, to put a few pages of extra material on the book and perhaps give links for folks to follow if they're interested in the topic?"

Traditionally, you'd issue a new edition with such information, but that seems like a hella work and expenditure, and small stuff like this should be the kind of thing you'd be able to stick somewhere online, if nothing else as a parking spot until you eventually publish a new edition.

I wonder if the Internet Archive would be interested in this kind of archival.