Add manpage

[tsimonq2]

When building the latest release for Lubuntu, the Debian package linter noted that the following binaries have no manpage:

• qtxdg-desktop-file-start
• qtxdg-iconfinder
• qtxdg-mat

The comment from @agaida in the packaging is:

# Yeah, we know

Can we address this without ignoring it? :)

[tsimonq2]

$ qtxdg-desktop-file-start -h
Usage: qtxdg-desktop-file-start [options] file [urls...]
QtXdg XdgDesktopFile start Tester

Options:
  -h, --help     Displays this help.
  -v, --version  Displays version information.

Arguments:
  file [urls...] desktop file to start and it's urls
$ qtxdg-iconfinder -h
Usage: qtxdg-iconfinder [options] [iconnames...]
QtXdg icon finder

Options:
  -v, --version  Displays version information.
  -h, --help     Displays this help.

Arguments:
  iconnames      The icon names to search for
$ qtxdg-mat -h
Usage: qtxdg-mat [options] command
QtXdg MimeApps Tool

Options:
  -h, --help     Displays this help.
  -v, --version  Displays version information.

Arguments:
  command        Command to execute.

Available commands:
  defapp    Get/Set the default application for a mimetype
  open      Open files with the default application
  mimetype  Determines a file (mime)type

Nice, so this is easy low-hanging fruit. :)