Talk about RP <-> TS communication under Privacy Considerations

[davidben]

We do leave the exact RP <-> TS protocol out of scope, so that it can slot into existing RP update protocols, but it's probably worth calling out a couple things here:

• The RP doesn't contact the TS on each TLS connection, only periodically and out-of-band
• There's no reason for the RP to tell the TS anything about TLS connections. The RP just says "give me the latest thing" and the TS passes it along

So the only information passed along is "I exist", same as any other periodic update protocol.

[bwesterb]

It's more than I exist: it's I'm online.