Mirroring patterns should be mentioned here. It's one of the fundamental tools in mania mapping. Hell, all you really need to say is something alone the lines of "Remember, any pattern mentioned here, including itch relevancy, can be mirrored."
If this is going to be the go-to tutorial on mania mapping basics (which it currently is), it would be good to cover all the basics, not just what you feel like covering.
As it stands it honesty sounds like you are telling people they can only go from left to right, which is entirely untrue. Even if you didn't intend it to come off that way (because mirroring is something you can generally assume people should understand if they're a decent mapper) it doesn't change the fact that this is specifically for newcomers, and you don't want to accidentally leave something that is misinterpreted by those new mappers. You need to be explicit about what you expect people to know coming in, even if you don't cover it at all.
Also "this is not part of the guide" is irrelevant if you're trying to make a good guide. If it's part of mapping basics, it should be part of the guide. Mirroring things is basic and one of those things new mappers should be reminded of. (I might be a bit... overzealous? here, wasn't trying to be an ass or anything <_<)