docs: trim the README to build and install

README.md

@@ -1,21 +1,7 @@
 # cutefish-dm
 
-The Cutefish display manager. It runs the login screen
-(`cutefish-compositor --login`) and the Wayland session the user picks, Cutefish
-or any other `wayland-sessions` entry such as GNOME or Plasma, with no black
-frame or console in between.
-
-The login screen runs on VT1 and the session on VT2, so every handover is a switch
-between two VTs that are already drawing. On a single VT the console would flash
-whenever a compositor exits.
-
-- `cutefish-dm` is the root daemon. The login screen talks to it over
-  `GREETD_SOCK` with greetd's protocol; `start_session` may name a
-  `wayland-sessions` id instead of a command.
-- `cutefish-dm-helper` runs PAM and the session for one login, like greetd's
-  session worker and sddm-helper.
-- `cutefish-session` calls `com.cutefish.DisplayManager.SwitchToGreeter` before
-  it logs out, so the login screen is already up when the session ends.
+The Cutefish display manager. It runs the login screen and starts the Wayland
+session the user picks.
 
 ## Dependencies
 
@@ -29,7 +15,7 @@ cmake --build build
 sudo cmake --install build
 ```
 
-The Debian package creates the login screen's user; a source install needs it once:
+A source install needs the login screen's user once:
 
 ```shell
 sudo adduser --system --group --home /var/lib/cutefish-greeter cutefish-greeter
@@ -42,8 +28,6 @@ sudo systemctl disable sddm
 sudo systemctl enable cutefish-dm
 ```
 
-Optional settings go in `/etc/cutefish-dm.conf`; see `daemon/config.cpp`.
-
 ## Tests
 
 ```shell