title: How to ignore files which are in repository?
body: <p>I have a file (<code>config.php</code>), that is already committed to a Git repository, but I want to ignore locally, i.e. I want that file to remain in repository, but force Git to ignore any changes to it.</p>
  <p>I put the file into <code>.gitignore</code>, but it is still marked as changed and Git still is attempting to commit changes to it, every time I commit something.</p>
  <p>Any ideas, what am I missing or doing wrong?</p>