[doc] Rewrite native script documentation
[doc] Rewrite native script documentation

Closes #13811

baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo