title: How to search nested Doc in Elasticsearch_dsl
body: <p>I have multiple indices on of them called Post with Nested document Comment.</p>
  <p>this is how my documents defined</p>
  <pre><code>class CommentDoc(InnerDoc):
      title = Text(analyzer=ngram_analyzer)
      content = Text(analyzer=ngram_analyzer)
  class PostDoc(Document):
      content = Text(analyzer=ngram_analyzer)
      comments = Nested(Icd10Doc)
      id = Integer()
  </code></pre>
  <p>this is how I'm doing the current search</p>
  <pre><code>s = Search(index=['post', 'blog', 'artical'])
  q = Q(&quot;multi_match&quot;, query=&quot;whatever&quot;, fields=['name', 'title', 'content'])
  s = s.query(q)
  </code></pre>
  <p>So how can I search the Post index using the nested Docs inside comments?</p>
  <p>what should I add to fields array?</p>