README: Update running a WM as the main unit

README.md

@@ -132,11 +132,14 @@ Target                       | Started when
 ### Starting the session
 
 A sessiond-based session should be started via a display manager, using
-the provided `sessiond.desktop` X session file.
+the provided `sessiond.desktop` Desktop Entry file.
 
 For example, configure `lightdm` to start a sessiond session by setting
 `user-session=sessiond` in `/etc/lightdm/lightdm.conf`.
 
+Alternatively, a window manager can be run directly via a custom Desktop Entry
+file. See [Running a window manager](#running-a-window-manager).
+
 ### Running services
 
 `sessiond-session.target` binds to `graphical-session.target` provided
@@ -192,6 +195,8 @@ ExecStopPost=/usr/bin/sessionctl stop
 WantedBy=graphical-session.target
 ```
 
+However, this is not necessary when running a window manager as described below.
+
 ### Running a window manager
 
 To use sessiond alongside a window manager, the session can be started with:
@@ -207,11 +212,7 @@ PartOf=graphical-session.target
 
 [Service]
 ExecStart=/usr/bin/twm
-ExecStopPost=/usr/bin/sessionctl stop
 Restart=always
-
-[Install]
-WantedBy=graphical-session.target
 ```
 
 A custom Desktop Entry can be used to run the window manager and session:
@@ -224,6 +225,9 @@ Exec=sessionctl run window-manager.service
 Type=Application
 ```
 
+This entry can be selected via the display manager or set as the default in its
+configuration file.
+
 ### Locking the session
 
 By default, the session is locked when it becomes idle and before sleeping.