I recently posted an answer to a challenge. I included a rather lengthy "how it's done" guide with the answer. I want to make the explanation available because I find it interesting and I hope a few others do, too. I don't really want to include the guide with the answer though because 1) it's really long, and 2) I kind of like the mystery without the "how to" staring you directly in the face. Is there another good place on codegolf to put it?
You could post it to an online fiddle site (Ideone, jsfiddle, etc.) with explanatory comments in the version there.
Then people are free to follow the link if they want to see how the sausage is made, but it's not in their face as they are reading the answer.
Or just blog about it and link to your blog. Past posts on meta.SO have established that is Ok if you're not being blatantly self-promotional or a huckster/shill.
You should keep it there, but make it code, so it will have it's own scroll bar (except on mobile). I wouldn't prefer external resources, as they can be down / lost / deleted, making the explanation unreachable.