DOC tweaks to plot_parc_values.py aesthetics
DOC tweaks to plot_parc_values.py aesthetics

bpinsard/PySurfer,effigies/PySurfer,Eric89GXL/PySurfer,nipy/PySurfer,diego0020/PySurfer,haribharadwaj/PySurfer,mwaskom/PySurfer