docs(README.md): increment readme

Author: luiz-nogueira

README.md

@@ -39,6 +39,7 @@ To create new injectors for your topics, you should create a new kubernetes depl
 - `ES_TIME_SUFFIX` Indicates what time unit to append to index names on Elasticsearch. Supported values are `day` and `hour`. Default value is `day` **OPTIONAL**
 - `KAFKA_CONSUMER_RECORD_TYPE` Kafka record type. Should be set to "avro" or "json". Defaults to avro. **OPTIONAL**
 - `KAFKA_CONSUMER_METRICS_UPDATE_INTERVAL` The interval which the app updates the exported metrics in the format of golang's `time.ParseDuration`. Defaults to 30s. **OPTIONAL**
+- `KAFKA_CONSUMER_WITH_KEY_AND_VALUE` If you would to combine the result message with the value present in the key. Defaults to false. **OPTIONAL**
 
 ### Important note about Elasticsearch mappings and types