See Configuring a remote for a fork.
git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git
See Syncing a fork
git fetch upstream
git checkout master
git merge upstream/master
See Configuring a remote for a fork.
git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git
See Syncing a fork
git fetch upstream
git checkout master
git merge upstream/master