The rawgit.com service which provides the dcoumentation does no longer exist

[caco3]

See https://rawgit.com/zevv/duc/master/doc/duc.1.html

It is lined to through https://duc.zevv.nl/

[caco3]

I don't know where the source files for https://duc.zevv.nl/ are stored or provided from.
I would suggest to use https://docs.github.com/pages and could help is you want.