Add documentation for serial plotter

I haven't found any documentation for the serial plotter, is there any?
For example, I've noticed that you can just print comma-separated (or space-separated) values, but I don't know if there's more to this (can I name the plots, doing something like `A=1 B=2`, for example? Also, are there other options to separate values? What values can I plot? etc).
This, combined with the fact that the serial plotter is kind of hidden, may make people not know it exists.