I'm having trouble figuring out what a "semantic pull request" is from that link, it's not a concept I've heard of before, and I'm interested. I mean, i assume it's some conventions for what goes in PR message, but what are they? Is there a better link?

In general, as a developer-consumer of them, I have found automatically-generated-from-commits changelogs to be not so useful, but I don't know if I've experienced any using the conventions you are recommending (which I dont' understand!).

In the small projects I write, I include links to the PR in the manually created CHANGELOG (the delta of which is part of the PR) simply by making the PR, then making another commit/ammend in the PR to add it's own url to the CHANGELOG. These are some extra steps, it's true.