RFC: Write a plan for Zebra Consensus Failure

[teor2345]

Motivation

We want to write a plan for how we'll deal with a Zebra consensus failure, and maybe other security issues.

We'll need this plan when users start relying on Zebra.

Tasks

• write a RFC about Zebra consensus failure
• move the final RFC to the Zebra Book
• maybe look at the tor security process - add link
• follow up on the ECC offer to share security issues - add ticket number

[dconnolly]

We might want to subsume this into #2001

[teor2345]

We've deferred this task a lot, we can do it if needed later.