Add write service to system_log (#9214)

source/_components/system_log.markdown

@@ -43,6 +43,16 @@ fire_event:
 
 To manually clear the system log, call this service.
 
+### {% linkable_title Service `write` %}
+
+Write a log entry
+
+| Service data attribute | Optional | Description                                                                     |
+| ---------------------- | -------- | ------------------------------------------------------------------------------- |
+| `message`              | no       | Message to log                                                                  |
+| `level`                | yes      | Log level: debug, info, warning, error, critical. Defaults to 'error'.          |
+| `logger`               | yes      | Logger name under which to log the message. Defaults to 'system_log.external'.  |
+
 ## {% linkable_title Events %}
 
 Errors and warnings are posted as the event `system_log_event`, so it is possible to write automations that trigger whenever a warning or error occurs. The following information is included in each event:
@@ -114,3 +124,24 @@ automation:
         message: '{{ trigger.event.data.message }}'
 ```
 {% endraw %}
+
+### {% linkable_title Writing to log %}
+
+This automation will create a new log entry when the door is opened:
+
+{% raw %}
+```yaml
+automation:
+  - alias: Log door opened
+    trigger:
+      platform: state
+      entity_id: binary_sensor.door
+      from: 'off'
+      to: 'on'
+    action:
+      service: system_log.write
+      message: 'Door opened!'
+      level: info
+```
+{% endraw %}
+