docs: update man page

Author: actions-user

duf.1

@@ -61,7 +61,7 @@ sort output by: mountpoint, size, used, avail, usage, inodes, inodes_used, inode
 style: unicode, ascii
 .TP
 \fB-theme\fP
-color themes: dark, light
+color themes: dark, light, ansi
 .TP
 \fB-usage-threshold\fP
 specifies the coloring threshold (yellow, red) of the usage bars as a floating point number from 0 to 1