3rd party repo policy followup

[Allan Day]

Hi everyone,

A little while ago, the Council very helpfully agreed to update the 3rd
party repo policy [1]. There are a couple of followup actions which I
wanted to make people aware of, in case they have comments:

1. Updates to the policy wording - see my PR here [2].
 2. A tentative design for the initial setup UI, which users will have to
use to enable the 3rd party repos [3].

Just let me know if you have feedback on either of these!

Thanks,

Allan