fix README

Signed-off-by: zirain <zirain2009@gmail.com>

Author: zirain

README.md

@@ -236,7 +236,7 @@ func main() {
 				"Video Ads",
 			},
 		}),
-		charts.PieSeriesShowLabel(),
+		charts.SeriesShowLabel(true),
 		// other options as desired...
 ```