* colorized-man-pages: Added hooks for commands dman and debman

`dman` and `debman` are tools from the package `debian-goodies` for
Debian systems (see https://packages.debian.org/stable/debian-goodies).
They can display man pages from manpages.debian.org or local debian
packages respectively.

README of the plugin is also updated.

* Simplify syntax for future changes

* Fix README syntax
Co-authored-by: Marc Cornellà <marc.cornella@live.com>