Mention KConfig.WindowStateSaver in Kirigami tutorial
Now that KConfig has exposed a QML component for managing window state (frameworks/kconfig!316 (merged)) and we're porting all our QML apps to use it (see for example plasma/discover!916 (merged), multimedia/elisa!620, and plasma/plasma-systemmonitor!308), the Kirigami app tutorial should include it.
Edited by Thiago Sueto