title: Gitignore does not update a file already on my repo
body: <p>I have a simple problem with my git :</p>
  
  <p>I have this file <strong>inc.conf.php</strong> on my repository on github.
  I don"t want to delete him from the repo, it's a basic config file.</p>
  
  <p>Now, on my local repo, I have the same file <strong>inc.cong.php</strong> with my own config, and I don"t want this file will be commited.</p>
  
  <p>So I create a .gitignore and I add <strong>inc.config.php</strong> in.
  (the .gitignore is commit and push on the repo)</p>
  
  <p>But when I update the file <strong>inc.config.php</strong> in local and tape <code>git status</code> :</p>
  
  <pre><code>On branch master
  Your branch is up-to-date with 'origin/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:   Swindle-Foundation5/inc.config.php
  
  no changes added to commit (use "git add" and/or "git commit -a")
  </code></pre>
  
  <p>But I don"t want to change the file on the repository from github.
  How can I do this ?</p>