Currently, when there are existing symlinks, the following happens:

• The existing hooks is left in place.
• Symlink creation for PHP Composter's hook fails.
• The user does not get notified of this happening, and might wonder why the PHP Composter action is not triggered.

To deal with this, we'd have two possible approaches:

1. Notify the user to do something about the existing hook and rerun composer install.
2. Rename/move the existing hook, and have PHP Composter shell script run this too.

Option 2 would automate this stuff and everything would just work, but might lead to a case where PHP Composter is removed, which causes both PHP Composter actions and previously installed Git hooks to be deactivated. There might be a way to hook into composer remove though...