add note about what the gold standard annotations table is (#2645)
add note about what the gold standard annotations table is (#2645)

* add note about what the gold standard annotations table is

noting that this data is for specific projects and was sliced out of classification table and long term can go, not till the projects finish / port to the new feedback subject metadata mechanism though.

* copy edits on the gold standard annotation class note

camallen/Panoptes,camallen/Panoptes,camallen/Panoptes,zooniverse/Panoptes,zooniverse/Panoptes,zooniverse/Panoptes,zooniverse/Panoptes,camallen/Panoptes