[anecdotal evidence] hashed sub-domains get blocked on some networks

[stevieflow]

I only know this from experience of the old super secret link, that in some circumstances the URL rendered would have to be checked by network admins, and sometimes "cleared" for use

This doesnt quite make sense, as every preview is at a different unique URL.

Rather than second guess, we can leave this here in case some users find network difficulties (maybe that was the issue in #20 ?)

Additionally - is it also possible to know if previews could be generated at d-preview.domain/[hash] rather than [hash].d-preview.domain (where we had full and total control over d-preview.domain

Thanks!

[xriss]

Subdomains where the simplest way to build things with minimal changes to the base code, so that's what I went with.

Any change would require more development time.