I have downloaded an archive of some large GitHub repository using *Download ZIP* link. It contained just the source code, so it wasn't a clone or a git repo anymore. Then I made some changes in this code on my disk and now I want to update it using the code of HEAD revision from the original GitHub repo (which has changed since I downloaded the ZIP file). But it's a large repo, so I don't want to download all the files, but just the modified ones.

Should I `git init` a new repo in my existing source code folder, then `git add .` and `git commit` then `git remote add origin https://github.com/someuser/someproject.git` and `git pull origin master`? Will this download only the modified files?