keyd: add example (#20211)

pages/linux/keyd.md

@@ -9,7 +9,7 @@
 
 - Display keypress information:
 
-`sudo keyd monitor`
+`sudo keyd {{[-m|monitor]}}`
 
 - Reset bindings and reload the configuration files in `/etc/keyd`:
 
@@ -19,6 +19,10 @@
 
 `keyd list-keys`
 
+- Check the detected configuration files for errors:
+
+`keyd check`
+
 - Create a temporary binding:
 
 `sudo keyd bind "{{pressed_key}} = {{output_key}}"`