문서 조회

GET [인덱스_이름]/_doc/[id값]

GET my_index/_doc/1

## 결과
{
  "_index": "my_index",
  "_id": "1",
  "_version": 2,
  "_seq_no": 2,
  "_primary_term": 1,
  "found": true,
  "_source": {
    "title": "hello elasticsearch!",
    "views": 1234,
    "public": true,
    "created": "2019-01-17T14:05:01/234Z"
  }
}