docs: add button with badge example

Author: astagi

src/app/badge/badge-example/badge-example.component.html

@@ -36,6 +36,10 @@ <h5>
       </h5>
 
       <h5>Link di esempio <a href="#" [itBadge]="selectedColor" [rounded]="isRounded">link</a></h5>
+      <button class="mb-5" [itButton]="'primary'">
+        Profilo <span [itBadge]="selectedColor" [rounded]="isRounded">9</span>
+        <span class="visually-hidden">Messaggi non letti</span>
+      </button>
     </div>
   </div>
 </div>