Thank you. I do know I have found an answer (not the answer), but I am here for finding a solution. On the other hand the above-mentioned answer shows no sign of impossibility to have linux-docs in the Manjaro repository as well.
I have also checked the linux-docs package in the Arch repository, and I am not expert, but it does not seem to be an insurmountable difficulty to solve this issue. My guess is the kernel packaging team probably has the authority to handle this problem. The aforesaid repo entry suggests few line of code in the PKGBUILD file to generate the docs automatically and the previously found answer tells also, there is not anything against to do so (“Manjaro is not distributing any docs yet for it’s kernels. We can consider to do so however.”).
The suspicious parts are make htmldocs in the build () section and the package-docs() section itself.
I am not familiar with the group dynamic or the a hierarchy of the Manjaro developer and maintainer team, so I am not sure where to keep searching for a solution for all.