Fix developer guide _meta/beat.yml instead of etc/beat.yml (elastic#4300

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docs/devguide/newbeat.asciidoc

@@ -351,7 +351,7 @@ countbeat:
 
 The config file is generated when you run `make setup` to <<setting-up-beat,set up the beat>>. The file contains
 basic configuration information. To add configuration options to your Beat, you need to update the Go structures in
-`config/config.go` and add the corresponding config options to `etc/beat.yml`.
+`config/config.go` and add the corresponding config options to `_meta/beat.yml`.
 
 For example, if you add a config option called `path` to the Go structures:
 
@@ -369,7 +369,7 @@ var DefaultConfig = Config{
 
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-You also need to add `path` to `etc/beat.yml`:
+You also need to add `path` to `_meta/beat.yml`:
 
 [source,yml]
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@@ -427,7 +427,7 @@ through the `client` variable.
 The `event := common.MapStr{}` stores the event in a json format, and `bt.client.PublishEvent(event)` publishes data to Elasticsearch.
 In the generated Beat, there are three fields in the event: @timestamp, type, and counter.
 
-When you add fields to the event object, you also need to add them to the `etc/fields.yml` file:
+When you add fields to the event object, you also need to add them to the `_meta/fields.yml` file:
 
 [source,yaml]
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