add first files in output/ and update artwork.org file.

I renamed the file referenced in artwork.org to
output/art-width-height-2023-03-21.png -- just making sure the files in output/
are linked correctly before moving on.

artwork.org

@@ -559,4 +559,4 @@ They should be =21 x 14.8 cm= and not =210 x 148 cm=. *I have updated the dimens
 on the live site.* I did not notice it until I saw the chart. Basically, the
 decimal point is was shifted one place to the right.
 
-[[file:output/artwork-width-height-2023-03-21.png]]
+[[file:output/art-width-height-2023-03-21.png]]