Adding comments to warn against updating the tna_timestamp for these 7 sites.

These sites were part of partial transitions of corporate content; these timestamps represent the pre-transition full-site TNA crawls. If the timestamp is changed/updated, URLs for these sites may present GOV.UK pages, rather than the desired original site URL. Consider using the custom archive link.
Merge pull request #593 from rjc123/newsites

Adding comments to warn against updating the tna_timestamp