update documentation with release 2.6.0

Author: dadoonet

README.md

@@ -7,7 +7,7 @@ for the unicast discovery mechanism and add S3 repositories.
 In order to install the plugin, run: 
 
 ```sh
-bin/plugin install elasticsearch/elasticsearch-cloud-aws/2.5.1
+bin/plugin install elasticsearch/elasticsearch-cloud-aws/2.6.0
 ```
 
 You need to install a version matching your Elasticsearch version: