[Klipper] Upate the klipper docbook after porting to QRegularExpression

Reviewers: Plasma, davidedmundson, apol, broulik, yurchor

Reviewed By: yurchor

Subscribers: yurchor, kde-doc-english, plasma-devel

Tags: Plasma, Documentation

Differential Revision: https://phabricator.kde.org/D28534