Ask new uploaders to link to their packages

[endgame]

New accounts are telling us what package they'd like to upload, which is good, but then they're emailing us cabal sdists, which is less good.

[endgame]

CI breakage doesn't look like my fault, at a glance.

[endgame]

Also the text is currently incoherent. I'll need to fix that before merge.

[endgame]

Okay, I think that reads better.

[endgame]

What needs to happen to get this merged?

[gbaz]

I'll merge it. No promises on when the next deploy will be however.

[endgame]

Any chance of a deploy sometime soon? We're still getting tarballs from prospective uploaders.