Added KDE's notes to the knowledge base

knowledge base/kde.md

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+# KDE
+
+## TL;DR
+
+```shell
+# Get from '~/.config/kinfocenterrc' the current value for the 'MenuBar' key in
+# the 'MainWindow' group.
+kreadconfig5 --file kinfocenterrc --group MainWindow --key MenuBar
+
+# Set into '~/.config/kdeglobals' a new value for the 'Show hidden files' key in
+# the 'KFileDialog Settings' group.
+kwriteconfig5 --file kdeglobals --group 'KFileDialog Settings' \
+  --key 'Show hidden files' --type bool true
+```
+
+## Further readings
+
+- [KDE Configuration Files]
+
+[kde configuration files]: https://userbase.kde.org/KDE_System_Administration/Configuration_Files
+
+## Sources
+
+- [Gsettings-like tools for KDE]
+
+[gsettings-like tools for kde]: https://askubuntu.com/questions/839647/gsettings-like-tools-for-kde