added more specific info about user scope (#72680)

in ref of #72674

lib/ansible/modules/systemd.py

@@ -60,9 +60,11 @@ options:
         description:
             - run systemctl within a given service manager scope, either as the default system scope (system),
               the current user's scope (user), or the scope of all users (global).
-            - "For systemd to work with 'user', the executing user must have its own instance of dbus started (systemd requirement).
-              The user dbus process is normally started during normal login, but not during the run of Ansible tasks.
+            - "For systemd to work with 'user', the executing user must have its own instance of dbus started and accessible (systemd requirement)."
+            - "The user dbus process is normally started during normal login, but not during the run of Ansible tasks.
               Otherwise you will probably get a 'Failed to connect to bus: no such file or directory' error."
+            - The user must have access, normally given via setting the ``XDG_RUNTIME_DIR`` variable, see example below.
+
         type: str
         choices: [ system, user, global ]
         default: system
@@ -124,6 +126,14 @@ EXAMPLES = '''
 - name: Just force systemd to re-execute itself (2.8 and above)
   systemd:
     daemon_reexec: yes
+
+- name: run a user service when XDG_RUNTIME_DIR is not set on remote login.
+  systemd:
+    name: myservice
+    state: started
+    scope: user
+  environment:
+    XDG_RUNTIME_DIR: "/run/user/{{ myuid }}"
 '''
 
 RETURN = '''