Update recommended and required protocol versions for "LinkAuth"

LinkAuth method 1 is the one where we pull the TLS master secrets out of the OpenSSL data structures and authenticate them with RSA. LinkAuth method 3 is the one where we use the RFC5705 key export mechanism and Ed25519 signatures; it is not supported in 0.2.9.

Right now we list method 1 as required for clients and relays. That's a problem, since we can't reasonably support it with NSS.

We should at least say that method 1 is not required for clients, and method 3 is recommended for everybody.

Should any method be required for relays? I don't think so currently, since we don't want to kick anybody off the network.

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