How to bring a branch of an open source project that you forked up-to-date with the master branch of the original project?.md

When creating a pull request on an project that you forked, you should rebase the master branch of the original repository on your branch and then create the pull request. Similarly, when the branch of a pull request has become out of date w.r.t the master branch (that is, the default branch), again, you should rebase the default branch of the original repository on your pull request's branch and then force push your branch. So, while you are on your pull request's branch:

git remote add upstream https://github.com/original-owner-of-the-project/project-name
git rebase upstream/master
git push -f