Fix duotone example missing "duotone" style hint

README.md

@@ -101,11 +101,13 @@ dependency_overrides:
 Duotone icons require special treatment. Instead of `FaIcon` a special class
 `FaDuotoneIcon` needs to be used. It allows to set the primary and secondary colors
 for the icon. If primary and / or secondary color are not defined, they will default
- to the standard `IconTheme` color.
+ to the standard `IconTheme` color. Please be aware that only duotone style icons
+ can be passed to this class.
+ 
 
 ```dart
 FaDuotoneIcon(
-  FontAwesomeIcons.abacus,
+  FontAwesomeIcons.duotoneAbacus,
   primaryColor: Colors.black.withOpacity(.4),
   secondaryColor: Colors.black,
 );