[Doc]Add note about _type setting change from doc to _doc

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 10.4.1
+ - [DOC] Added note about `_type` setting change from `doc` to `_doc` [#884](https://github.com/logstash-plugins/logstash-output-elasticsearch/pull/884)
+
 ## 10.4.0
  - Fixed default index value [#927](https://github.com/logstash-plugins/logstash-output-elasticsearch/pull/927)
 

docs/index.asciidoc

@@ -21,6 +21,21 @@ include::{include_path}/plugin_header.asciidoc[]
 
 ==== Description
 
+.Compatibility Note
+[NOTE]
+================================================================================
+When connected to Elasticsearch 7.x, modern versions of this plugin
+use the required `_doc` document-type when inserting documents.
+
+If you are using an earlier version of Logstash and wish to connect to
+Elasticsearch 7.x, first upgrade Logstash to version 6.8 to ensure it
+picks up changes to the Elasticsearch index template.
+
+If you are using a custom <<plugins-{type}s-{plugin}-template>>,
+ensure your template uses the `_doc` document-type before
+connecting to Elasticsearch 7.x.
+================================================================================
+
 .Compatibility Note
 [NOTE]
 ================================================================================

logstash-output-elasticsearch.gemspec

@@ -1,6 +1,7 @@
 Gem::Specification.new do |s|
   s.name            = 'logstash-output-elasticsearch'
-  s.version         = '10.4.0'
+  s.version         = '10.4.1'
+
   s.licenses        = ['apache-2.0']
   s.summary         = "Stores logs in Elasticsearch"
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program"