Add extra card class attribute in README.md

The README.md has been updated to include the use of the 'extraCardsAttributes' property in the instructions for users. This property allows users to add extra class attributes to the card HTML element in the customizable radio deck implementation using TailwindCSS utilities.

README.md

@@ -82,6 +82,9 @@ public static function form(Form $form): Form
                 ->gap('gap-5') // Gap between Icon and Description (Any TailwindCSS gap-* utility)
                 ->padding('px-4 px-6') // Padding around the deck (Any TailwindCSS padding utility)
                 ->direction('column') // Column | Row (Allows to place the Icon on top)
+                ->extraCardsAttributes([ // Extra Attributes to add to the card HTML element
+                    'class' => 'rounded-xl'
+                ])
                 ->extraOptionsAttributes([ // Extra Attributes to add to the option HTML element
                     'class' => 'text-3xl leading-none w-full flex flex-col items-center justify-center p-4'
                 ])