If the problem is that your fork just looks like the upstream and you can't modify README in there because this would make sending patches to upstream painful,

If the problem is that your fork just looks like the upstream and you can't modify README in there because this would make sending patches to upstream painful, you could: - create a new branch in your fork, aside from original master/main (possibly a bare orphaned branch (with 0 commits)) - set it as default branch in repo settings - then in README.md of the new default branch, explain your contributions to the upstream (possibly with a link to github.com/<repo>/contributions?user=<yourname>)