Example notebook: Clarify how to set which workflow to postprocess

[gcapes]

First, specify the workflow you would like to post-process by changing the path string of the workflow variable.

It looks like the user should actually change the workflow_dir variable?

[Gbowker]

Yes at the moment the intention is for the user to just change the workflow_dir string variable - maybe there is a better way via python opening a explorer window asking the user to select the workflow directory?
There is tkinter for this, but it requires changing the matplotlib backend which could effect the plotting functions.

[gcapes]

I guess you could use a GUI, but what I meant was that it wasn't explicit which variable the user should set (i.e. that "the workflow variable" refers to workflow_dir).