Merge branch 'remove-compat-notes' of github.com:karenzone/logstash-output-elasticsearch into remove-compat-notes

Author: karenzone

docs/index.asciidoc

@@ -24,6 +24,9 @@ include::{include_path}/plugin_header.asciidoc[]
 If you plan to use the Kibana web interface to analyze data transformed by Logstash, use the Elasticsearch output plugin
 to get your data into Elasticsearch. 
 
+This output only speaks the HTTP protocol as it is the preferred protocol for interacting with Elasticsearch.
+In previous versions it was possible to communicate with Elasticsearch through the transport protocol, which is now reserved for internal cluster communication between nodes https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-transport.html. This has been deprecated in Elasticsearch 7.0.0 and will be removed in 8.0.0 https://www.elastic.co/guide/en/elasticsearch/reference/current/java-clients.html
+
 You can learn more about Elasticsearch at <https://www.elastic.co/products/elasticsearch>
 
 .Compatibility Note