adding to gitignore doesn't ignore code example

Example: Why doesn't Git ignore my specified file?

In order to actually ignore the file, you have to untrack it and remove it from the repository. You can do that by using git rm --cached sites/default/settings.php. This removes the file from the repository without physically deleting the file (that’s what the --cached does). After committing that change, the file will be removed from the repository, and ignoring it should work properly.