clarify the features in the readme file

Author: dbu

README.md

@@ -5,7 +5,8 @@ This bundle provides integration with [Elasticsearch](http://www.elasticsearch.o
 Symfony. Features include:
 
 - Integrates the Elastica library into a Symfony environment
-- Automatically generate mappings using a serializer
+- Use JmsSerializer or Symfony Serializer to convert between PHP objects and Elasticsearch data
+- Index configuration for Elasticsearch, or send data without configuration to use the dynamic mapping feature of Elasticsearch
 - Listeners for Doctrine events for automatic indexing
 
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