Add credits section

Add a credits box below the current section with information about Bulgarian Solitaire, its origins, and resources for further learning.

src/components/BulgarianSolitaire.tsx

@@ -428,6 +428,14 @@ const BulgarianSolitaire: React.FC<BulgarianSolitaireProps> = ({ showSocialShare
         </ul>
       </div>
 
+      {/* Credits */}
+      <div className="bg-muted/30 rounded-lg p-6 space-y-4">
+        <h3 className="text-lg font-semibold">Credits:</h3>
+        <p className="text-sm text-muted-foreground">
+          Find out more about Bulgarian Solitaire on Wikipedia. I learned of this game from Akash Kumar, who very kindly walked me through the argument found in Peter Winkler's beautiful puzzle book, available here. The game was introduced by Martin Gardner.
+        </p>
+      </div>
+
       {showSocialShare && (
         <SocialShare 
           title="Bulgarian Solitaire - Interactive Mathematical Puzzle"