Update example.config.toml

It seems like 
# fee_percent=0.04
# reserve_fee_min=4

need to be under [lnd] as well 
got an error message when they weren't under [lnd]

close if not.

crates/cdk-mintd/example.config.toml

@@ -66,6 +66,8 @@ reserve_fee_min = 1
 # address = ""
 # macaroon_file = ""
 # cert_file = ""
+# fee_percent=0.04
+# reserve_fee_min=4
 
 # [fake_wallet]
 # supported_units = ["sat"]