title: Why do I get "panicked at 'not currently running on the Tokio runtime'" when using block_on from the futures crate?
body: <p>I'm using the example code on elastic search's blog post about their new crate and I'm unable to get it working as intended. The thread panics with <code>thread 'main' panicked at 'not currently running on the Tokio runtime.'</code>.</p>
  
  <p>What is the Tokio runtime, how do I configure it and why must I?</p>
  
  <pre><code>use futures::executor::block_on;
  
  async elastic_search_example() -&gt; Result&lt;(), Box&lt;dyn Error&gt;&gt; {
      let index_response = client
          .index(IndexParts::IndexId("tweets", "1"))
          .body(json!({
              "user": "kimchy",
              "post_date": "2009-11-15T00:00:00Z",
              "message": "Trying out Elasticsearch, so far so good?"
          }))
          .refresh(Refresh::WaitFor)
          .send()
          .await?;
      if !index_response.status_code().is_success() {
          panic!("indexing document failed")
      }
      let index_response = client
          .index(IndexParts::IndexId("tweets", "2"))
          .body(json!({
              "user": "forloop",
              "post_date": "2020-01-08T00:00:00Z",
              "message": "Indexing with the rust client, yeah!"
          }))
          .refresh(Refresh::WaitFor)
          .send()
          .await?;
      if !index_response.status_code().is_success() {
          panic!("indexing document failed")
      }
  }
  
  fn main() {
      block_on(elastic_search_example());
  }
  </code></pre>