title: Add previously ignored directory to Git repository
body: <p>My <code>.gitignore</code> file looks like:</p>
  
  <pre><code>html/
  cache/
  resources/
  # Temp files often created by editors
  *.~
  </code></pre>
  
  <p>I know wish to start tracking a specific directory in html, so I add `!html/support/</p>
  
  <pre><code>html/
  cache/
  resources/
  # Temp files often created by editors
  *.~
  # Track support
  !html/support/
  </code></pre>
  
  <p>After doing so, however, Git still doesn't seem to track html/support/ and all its children.</p>
  
  <p>How do I add a previously ignored directory to Git repository?</p>