JRuby is missing manpages, at least for the main JRuby executable.
In the Debian package we ship a very old hand-generated manpage, but it's a struggle to keep it up to date.
The manpages could either be maintained in markdown or reStructured text format, then converted to groff at build-time, or, another common method of generating a manpage is using the help2man tool which builds a rudimentary manpage from the executable's --help information.
FWIW C-Ruby ships a great manpage: https://manpages.debian.org/trixie/ruby/ruby.1.en.html
JRuby is missing manpages, at least for the main JRuby executable.
In the Debian package we ship a very old hand-generated manpage, but it's a struggle to keep it up to date.
The manpages could either be maintained in markdown or reStructured text format, then converted to groff at build-time, or, another common method of generating a manpage is using the
help2mantool which builds a rudimentary manpage from the executable's--helpinformation.FWIW C-Ruby ships a great manpage: https://manpages.debian.org/trixie/ruby/ruby.1.en.html