Instruction on creating a mapping

[AmberSJones]

It's not initially clear how to add, edit, or delete a mapping (done by double clicking a column in the file display). Should we add buttons or some text that tells the user to double click?

[kwuz]

I'd prefer to make the function evident from the design, but I don't know how feasible that is at this point. I'll play around with different labels and try to find something that looks good.