title: How to use warm_start
body: <p>I'd like to use the <code>warm_start</code> parameter to add training data to my random forest classifier. I expected it to be used like this:</p>
  
  <pre><code>clf = RandomForestClassifier(...)
  clf.fit(get_data())
  clf.fit(get_more_data(), warm_start=True)
  </code></pre>
  
  <p>But the <code>warm_start</code> parameter is a constructor parameter. So do I do something like this?</p>
  
  <pre><code>clf = RandomForestClassifier()
  clf.fit(get_data())
  clf = RandomForestClassifier (warm_start=True)
  clf.fit(get_more_data)
  </code></pre>
  
  <p>That makes no sense to me. Won't the new call to the constructor discard previous training data? I think I'm missing something.</p>