Improve documentation around Regex-based test steps

the SCPI and Process steps both uses regular expressions to do some simple parsing of the output, but actually the behavior is a bit surprising or at least not obvious.

Lets say the output of a SCPI step was:

"1.0, 2.0, 3.0"

In order to parse this, id expect this to be enough:

Regex: ([^,]+),?
Column Names: X, Y, Z
Behavior: Groups as Columns

This however gives an error saying the the number of columns does not match the number of groups. The regex for this means that I will instead get three rows with one column in each.

To do what I want I have to do like this:

Regex: ([^,]+),([^,]+),?([^,]+)
Column Names: X, Y, Z
Behavior: Groups as Columns

I think we should document the behavior with some examples or find more intuitive behaviors.