title: scikit-learn add training data
body: <p>I was looking at the training data available in <code>sklearn</code> at <a href="http://scikit-learn.org/stable/datasets/twenty_newsgroups.html" rel="nofollow">here</a>. As per documentation, it contains 20 classes of documents, based on some newsgroup collection. It does a fairly good job of classifying documents belonging to those categories. However, I need to add more articles for  categories, like cricket, football, nuclear physics, etc.</p>
  
  <p>I have set of documents for each class ready, like <code>sports -&gt; cricket</code>, <code>cooking -&gt; French</code>, etc.. How do I add those documents and classes in <code>sklearn</code> so that the interface which now returns 20 classes will return those 20 plus the new ones as well? If there is some training that I need to do, either through <code>SVM</code> or <code>Naive Bayes</code>, where do I do it before adding it to the dataset?</p>