I don't call it "art", but I've been putting textual diagrams into documentation lately, and I think it can be very helpful.

For example, I added a diagram to the Phoenix Channels guide, showing how the implementation works: https://github.com/phoenixframework/phoenix/blob/master/guid...

I use Monodraw (https://monodraw.helftone.com/), which lets you work with boxes, arrows, etc as objects in layers, and export to ASCII or Unicode. ASCIIFlow (http://asciiflow.com/) is a simpler alternative.