Update kde.md: include note about VTs and wayland

src/config/graphical-session/kde.md

@@ -19,6 +19,19 @@ If you wish to start an X-based session from the console, use
 [startx](./xorg.md#startx) to run `startplasma-x11`. For a Wayland-based
 session, run `startplasma-wayland` directly.
 
+## SDDM
+
+Note that if you are configuring SDDM to [run under wayland][sddm-wayland],
+you will need to ensure the first virtual terminal is not consumed by
+`agetty`:
+
+```
+rm /var/service/agetty-tty1
+```
+
+Doing this is **not required** when running SDDM under X11 (which is the
+default.)
+
 ## Dolphin
 
 Dolphin is the default file manager of the KDE desktop environment. It can be
@@ -32,3 +45,5 @@ package. If you want video thumbnails, the `ffmpegthumbs` package is also
 necessary. Enable previews in "Control" -> "Configure Dolphin" -> "General" ->
 "Previews" by checking the corresponding boxes. File previews will be shown for
 the selected file types after clicking "Preview" in Dolphin's toolbar.
+
+[sddm-wayland]: https://wiki.archlinux.org/title/SDDM#Running_under_Wayland