Add DUB man pages to the released archive

[dlangBugzillaToGithub]

Seb reported this on 2018-02-11T19:58:11Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18424

Description

DUB now provides man pages:

https://github.com/dlang/dub/pull/1342

It's probably a good idea to ship them with the release archives.
See also:

https://github.com/dlang/dub/issues/855