I would suggest git, but only because I have more experience using it. SVN works just fine as well, I just don't like the most popular client for it (TortoiseSVN). If you do decide to use git, you can just set it up in the same directory you're currently working in, so nothing would change as far as any other programs/pipelines are concerned. There would just be a .git directory next to the .txt files, which you don't even have to look at manually. You'll also need a host, like github, gitlab or bitbucket. They're all free, I've used all three extensively, and there's not much to recommend one over the other in my view. Any of them would work fine. Github doesn't give you free private repos, but it does have the best tool support (I think). I could post a little tutorial, if you'd like.