title: cannot add folder to gitignore file
body: <p>My <code>.gitignore</code> file is the following:</p>
  
  <pre><code>$ cat .gitignore
  Index/
  Index/LOG
  </code></pre>
  
  <p>I added <code>.gitignore</code> file to repo, commit and even push. But <code>git status</code> permanently shows:</p>
  
  <pre><code># On branch master
  # Changes not staged for commit:
  #   (use "git add &lt;file&gt;..." to update what will be committed)
  #   (use "git checkout -- &lt;file&gt;..." to discard changes in working directory)
  #
  #   modified:   Index/LOG
  #
  </code></pre>
  
  <p>So how to exclude whole <code>Index</code> folder from git repository forever?</p>