document log config syntax, don't give example

Because the old one was stale. Shocking!

conduit-example.toml

@@ -51,7 +51,11 @@ enable_lightning_bolt = true
 trusted_servers = ["matrix.org"]
 
 #max_concurrent_requests = 100 # How many requests Conduit sends to other servers at the same time
-#log = "warn,state_res=warn,rocket=off,_=off,sled=off"
+
+# Controls the log verbosity. See also [here][0].
+#
+# [0]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html#directives
+#log = "..."
 
 address = "127.0.0.1" # This makes sure Conduit can only be reached using the reverse proxy
 #address = "0.0.0.0" # If Conduit is running in a container, make sure the reverse proxy (ie. Traefik) can reach it.