This isn’t an update request, but rather an add request: linux-docs.
The Arch kernel is not in the Manjaro repo, therefore neither are it’s docs.
The kernel comes directly from kernel.org if I understand the git PKGBUILD correctly.
I don’t know how this is done, but whether ubuntu/lm, opensuse, they all had the linux kernel specific documentation. It’s available online, but I’m offline often. I’m missing it I have alternative methods, but I was looking here first.