Although there are two documentation options (DOCS and DOXYGEN), neither of them installs the full documentation.
This means that menu options for a manual do not work in kicad, eeschema and pcbnew.
These documents come in a separate distfile, kicad-doc-x.y.z.tar.gz.
Given the size of the distribution, perhaps this could be a separate port?
A commit references this bug:
Date: Fri Jun 21 13:52:02 UTC 2019
New revision: 504800
cad/kicad-doc: online help files and documentation for cad/kicad
Reported by: bob at eager dot cx
You're right (that demonstrates that you're the first one to try to use the online help). Here it is, cad/kicad-doc at ports r504800
I can't get chinese and polish language files to build, so I just hope we can do without them for the time being.