Update kde.md: include note about VTs and wayland

Author: SamWilsn

src/config/graphical-session/wayland.md

@@ -45,6 +45,21 @@ accessing input devices. In Void systems, this requires a seat manager service,
 which can be either elogind or seatd. Enabling them is explained in the
 ["Session and Seat Management"](../session-management.md) session.
 
+### Display Managers
+
+#### SDDM
+
+Note that if you are configuring SDDM to [run under
+wayland](https://wiki.archlinux.org/title/SDDM#Running_under_Wayland), you will
+need to ensure the first virtual terminal is not consumed by `agetty`:
+
+```
+touch /etv/sv/agetty-tty1/down
+```
+
+Doing this is **not required** when running SDDM under X11 (which is the
+default.)
+
 ### Native applications
 
 [Qt5](https://wayland.freedesktop.org/qt5.html)-based applications require