Background

It's unclear to many people what sphinxreplay.db is for.

Context

Replying to the question: "What is sphinxreplay.db for", on Slack:
@Roasbeef : "Security: it prevents replays of onion packets, w/o this ppl can collect onion packetrs then re-inject them and see where they travel to attempt to de-annon"
@Roasbeef : "I think we might be the only impl that handles them properly, have been meaning to add more details to the spec on this front."

Request

Adding more docs / more info in specs would be good 💯