Adjust label in the settings page for changed preview behaviour
Summary: Requested by https://phabricator.kde.org/D15138#318904
Test Plan: Opened the preview settings, label text changed.
Reviewers: Dolphin, elvisangelaccio
Reviewed By: Dolphin, elvisangelaccio
Subscribers: ngraham, markg, broulik, kfm-devel, elvisangelaccio
Tags: Dolphin
Differential Revision: https://phabricator.kde.org/D15216