How to draw a Circos track legend

In this guide Circos been shown how to set the interval between the two chromosomes that in this area it was possible to accommodate the legend of the track.
_{(source: circos.ca )}

As in the example above, but I can't find an explanation on how to draw the text there like a right circle.

Is it possible to draw a track legend using a config file, or do I need to use a graphics editor to add text manually to the output image?