title: How to correctly import operators from the `rxjs` package
body: <p>I am confused how to import those operators. Some I can import with 
  <code>import 'rxjs/add/operator/do';</code> and some I can not. For ex, this does not work:
  <code>import 'rxjs/add/operator/map';</code> (I checked in rxjs/add/operator, map exists there). </p>
  
  <p>Essentially what I am trying to do is to reproduce this in Angular4:</p>
  
  <pre><code>var requestStream = Rx.Observable.just('https://api.github.com/users');
  
  var responseStream = requestStream
    .flatMap(function(requestUrl) {
      return Rx.Observable.fromPromise(jQuery.getJSON(requestUrl));
    });
  
  responseStream.subscribe(function(response) {
    // render `response` to the DOM however you wish
  });
  </code></pre>
  
  <p>I also want to know how to deal with <code>just</code> operator, since I can not see it in rxjs/add/operator...</p>
  
  <p>Thanks for any help</p>