Update draft-pauly-v6ops-happy-eyeballs-v3.md

draft-pauly-v6ops-happy-eyeballs-v3.md

@@ -465,7 +465,7 @@ Host" {{!RFC6535}} but is implemented inside the Happy Eyeballs library.
 When an IPv4 address is passed into the library instead of a
 hostname, the device queries the network for the NAT64 prefix using
 "Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis"
-{{!RFC7050}}, or uses PREF64s received from Router Advertisements.
+{{!RFC7050}}, or uses PREF64s received from Router Advertisements {{!RFC8781}}.
 It then synthesizes an appropriate IPv6 address (or
 several) using the encoding described in "IPv6 Addressing of IPv4/
 IPv6 Translators" {{!RFC6052}}. The synthesized addresses are then