document node_id setting in sample ircd_config.toml

bin/ircd/ircd_config.toml

@@ -24,6 +24,9 @@ outbound_connections=5
 ## Seed nodes to connect to 
 seeds=["tls://irc0.dark.fi:11001", "tls://irc1.dark.fi:11001"]
 
+## Only used for debugging. Compromises privacy when set.
+#node_id = "foo"
+
 ## these are the default configuration for the p2p network
 #manual_attempt_limit=0
 #seed_query_timeout_seconds=8