In the Default UI, go to "Dimension / Leader".
Tab into the "Text" field and insert the text you want to display, then Enter.
The first snap places the arrowhead end of the Leader.
The second snap places the Text area.
"Alt+F" to finish.
V17—V21, 2015, 2016, 2017
Designer, Deluxe, Expert, Basic, Platinum
Windows 10, 64-bit