Update app.py

app.py

@@ -22,7 +22,10 @@ def read_root():
         <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
         <script src="/static/chessboard-1.0.0.min.js"></script>
         <script>
-            var board = Chessboard('board', 'start');
+            var board = Chessboard('board', {
+                position: 'start',
+                pieceTheme: '/static/img/chesspieces/wikipedia/{piece}.png'
+            });
         </script>
     </body>
     </html>