Example.pm template: freshener updates

- Point to metadata docs to help fill out section.
- Reorganize metadata into same order as docs.
- Remove "icon_url" and "source" which do not generally apply to
  Goodies.
- Better example strings for the `attribution` section.
- Use "guard" before "work" in example code.

If and when this is vetted and merged, I will make similar updates to the Spice repository (including the previous explicit caching changes.)