update nats docs

docs/docs/producers.md

@@ -222,13 +222,13 @@ The producer uses the [AWS SQS SDK](http://docs.aws.amazon.com/AWSJavaSDK/latest
 
 # Nats
 ***
-To produce messages to Nats, you can have the configuration specify in `config.properties`.
-
-The configurable properties are:
+The configurable properties for nats are:
 
 - `nats_url` - defaults to **nats://localhost:4222**
 - `nats_subject` - defaults to **%{database}.%{table}**
-  - This interpolated string config controls the subject hierarchies, where `%{database}` and `%{table}` and `%{type}` are placeholders that will be substituted at runtime. All non alphanumeric characters, all dots, all whitespaces, contained in the database, table or type will be replaced by underscores.
+
+`nats_subject` defines the Nats subject hierarchy to write to.  [Topic substitution](/producers#topic-substitution) is available.
+All non-alphanumeric characters in the substitued values will be replaced by underscores.
 
 # Google Cloud Pub/Sub
 ***