[kde-doc-english] New user guide: add a link the main list about KDE mailing lists

[Nicolas Goutte]

In the new user guide, in the section "Getting Help" 
(http://users.ox.ac.uk/~chri1802/kde/userguide-tng/getting-help.html )
There is a list of the 2 most importnat mailing lists of KDE, but now link to 
http://www.kde.org/mailinglists.

However that might be helpful, especially for non-Linux users who wants to 
find the mailinglist about KDE on their prefered OS.

Have a nice day!