Secure Boot and Microsoft CA Rollover - user-facing documentation

I previously wrote some advice for developers and distributions about the upcoming Microsoft CA Rollover, and I hope that was useful for people. I've now also added some user-facing documentation about the CA rollover in the Debian wiki at https://wiki.debian.org/SecureBoot/CAChanges . I've added guidance on managing certificate updates on Debian systems: how to check if a system needs those…