There is a way to show that information in the chart labels. You can eval your report field to include the total count for that field, the percentage, or whatever else you want to see and it will show up in the pie chart label for that slice:
your search | top YourField limit=20 | eval YourField=YourField." (".count.") ".percent."%"
Remove the count portion of the eval if you're not interested in it.
However, there's no way I know of to make the values or percentages show up inside each slice of the pie chart.
