Add File Exchange badge to README

Add the File Exchange badge to README.md with a link to the File Exchange submission.

Author: ViseDanya

README.md

@@ -1,5 +1,7 @@
 # Bubble Pie Chart
 
+[![View Bubble Pie Chart on File Exchange](https://www.mathworks.com/matlabcentral/images/matlab-file-exchange.svg)](https://www.mathworks.com/matlabcentral/fileexchange/98874-bubble-pie-chart)
+
 Version: 1.0
 
 bubblePieChart Creates a bubble pie chart.