Document how to config the greeter

README.md

@@ -1,3 +1,33 @@
 # Dotfiles
 
 Managed with [chezmoi](https://www.chezmoi.io)
+
+## Greeter
+
+I use greetd with gtkgreet as the greeter/login manager.  Because this is
+installed and configured as a system level service, its configuration cannot
+be managed by chezmoi.  Thankfully, when using cage, it's as straightforward
+as using the following configuration file:
+
+```toml
+[terminal]
+# The VT to run the greeter on. Can be "next", "current" or a number
+# designating the VT.
+vt = 1
+
+# The default session, also known as the greeter.
+[default_session]
+
+# `agreety` is the bundled agetty/login-lookalike. You can replace `/bin/sh`
+# with whatever you want started, such as `sway`.
+command = "GTK_THEME='Adwaita:dark' cage -s -- gtkgreet --background /usr/share/backgrounds/archlinux/wild.png --layer-shell"
+
+# The user to run the command as. The privileges this user must have depends
+# on the greeter. A graphical greeter may for example require the user to be
+# in the `video` group.
+user = "greeter"
+```
+
+This only requires installing greetd, gtkgreet, cage and the archlinux
+backgrounds packages.  Unlike the setup with sway, this doesn't require
+a loose formation of configuration files.