Documents updating base boxes for upgrade scenario
Documents updating base boxes for upgrade scenario

Conferred with @msheiny on the manual steps. Ideally we'd automate even
these, via inspecting checksums and modifying the JSON file
programatically, but the manual changes are only necessary after each SD
release, which isn't a terrible burden right now.

heartsucker/securedrop,heartsucker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,heartsucker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop