Add man documentation for spacing config option

man/waybar.5.scd.in

@@ -64,6 +64,10 @@ Also a minimal example configuration can be found on the at the bottom of this m
 	typeof: integer ++
 	Margins value without units.
 
+*spacing* ++
+	typeof: integer ++
+	Size of gaps in between of the different modules.
+
 *name* ++
 	typeof: string ++
 	Optional name added as a CSS class, for styling multiple waybars.