How can I stop .gitignore from appearing in the list of untracked files?
The .gitignore file should be in your repository, so it should indeed be added and committed in, as git status suggests. It has to be a part of the repository tree, so that changes to it can be merged and so on.
So, add it to your repository, it should not be gitignored.
If you really want you can add .gitignore to the .gitignore file if you don't want it to be committed. However, in that case it's probably better to add the ignores to .git/info/exclude, a special checkout-local file that works just like .gitignore but does not show up in "git status" since it's in the .git folder.
If you want to store the list of ignored files outside of your Git tree, you can use the .git/info/exclude file. It is applied only to your checkout of the repo.
You could actually put a line .gitignore into your .gitignore file. This would cause the .gitignore file to be ignored by git. I do not actually think this is a good idea. I think the ignore file should be version controlled and tracked. I'm just putting this out there for completeness.