Suggestion: Keep requirement to offer UDP transport

[weiss]

The README file currently says:

The requirement to have insecure transports to get a 'Great' score is likely to go away.

I think it actually makes sense to recommend offering UDP (and maybe unencrypted TCP) transports, since TLS encryption easily adds noticeable latency compared to UDP. As WebRTC calls are end-to-end encrypted and Matrix uses ephemeral TURN credentials, TLS usage adds no security (and the link between TURN server and peer uses unencrypted UDP either way). The corner case for which offering TLS (on port 443) does make sense is as a fallback for circumventing restrictive firewalls. But usually, UDP is preferable.