Add valueset generation/refresh information and spreadsheet

[bryantaustin13]

add to the vocabulary/valueset folder a "source" folder with the most recent copy of that spreadsheet and a README.md that includes the specific command to run to do the refresh and a link to that documentation for more information.
And an explanation of the fact that when this refreshes from the Master link in Google (put the link there too), that we update the copy of that in the IG and that that's part of the commit of the refresh.