To be clear right up front, since there are many similar-sounding questions around: I DON'T want to track the file.
My use case is that I have a "template" file that developers need to fill in with information. I don't want developers to go committing their changes to this file - they get the file on clone, make their own local changes, and those changes are just that: local. However, I'm not really sure how to get the file into my repo in the first place. Also, I might want to make occasional changes to the template file, but I'd prefer that I have to jump through hoops to do so, so that neither I nor anyone else accidentally commits their secret info.
How can I make commits to an un-tracked file in a git repo?