EnableProposed from wiki needs migrating #344
Description
https://wiki.ubuntu.com/Testing/EnableProposed, which is used in the standard comment by the SRU team to ask for testing pkgs in -proposed*, needs to be brought over (and updated) from the wiki to this docs set.
As part of that, the following page should also be a) migrated (what's needed of it) and b) deprecated: https://wiki.ubuntu.com/QATeam/PerformingSRUVerification
Additionally, https://wiki.ubuntu.com/StableReleaseUpdates should be updated to point to this docs set as opposed to the old SRU docs location (even though there are redirects in place, it's still potentially confusing).