[DOCS] Add blurb about data_path not needing to include index name

Resolves #11497
(node.enable_custom_paths is no longer used)

docs/reference/indices/shadow-replicas.asciidoc

@@ -51,7 +51,7 @@ curl -XPUT 'localhost:9200/my_index' -d '
         "number_of_replicas" : 4,
         "data_path": "/opt/data/my_index",
         "shadow_replicas": true
-    } 
+    }
 }'
 --------------------------------------------------
 
@@ -63,6 +63,9 @@ ensure that the Elasticsearch process has the correct permissions to read from
 and write to the directory used in the `index.data_path` setting.
 ========================
 
+The `data_path` does not have to contain the index name, in this case,
+"my_index" was used but it could easily also have been "/opt/data/"
+
 An index that has been created with the `index.shadow_replicas` setting set to
 "true" will not replicate document operations to any of the replica shards,
 instead, it will only continually refresh. Once segments are available on the