Support the onboarding of couriers during an Internet blackout

[gnarea]

Is your feature request related to a problem?

Yes. Many potential couriers may not have heard about it until they found themselves in an Internet blackout, but they should still be able to start relaying data without the Internet.

Describe the solution you'd like

A "Courier's Pack": A collection of some/all of the following files:

• The signed APK for Android (https://github.com/relaycorp/relaynet-courier-android; see https://issuetracker.google.com/issues/180927886)
• The signed installer for Windows. (https://github.com/relaycorp/relaynet-courier-desktop)
• A multi-lingual PDF to explain the job of a courier and how to install the apps. This PDF should ideally be signed by Relaycorp so that people can be certain of its authenticity if they open it with Acrobat Reader.
• The Relaynet User's Pack (Support the onboarding of users during an Internet blackout #1)

The files above could also be distributed over BitTorrent/IPFS and sneakernets like El Paquete Semanal.