unbound/plain-dns64.conf: add Google DNS

etc/unbound/unbound.conf.d/plain-dns64.conf

@@ -3,9 +3,14 @@
 
 forward-zone:
     name: "."
+
     # Trex DNS64/NAT64 <http://www.trex.fi/2011/dns64.html>
+    # > The generated AAAA records point to address blocks in TREX's public
+    # address space 2001:67c:2b0::/48 so they are usable from anywhere on
+    # the Internet.
     forward-addr: 2001:67c:2b0::4
     forward-addr: 2001:67c:2b0::6
-# Google is missing, I imagine they would have the same range, but as this
-# is plaintext and I only have DS (& DS lite) hosts, this file is not a
-# priority for me.
+
+    # Google DNS64 for 64:ff9b::/96 (reserved NAT64 space)
+    #forward-addr: 2001:4860:4860::6464
+    #forward-addr: 2001:4860:4860::64