git branch --set-upstream-to <remote-branch>

// example
git branch --set-upstream-to origin feature-branch

// show up which remote branch a local branch is tracking
git branch -vv

// short version to set upstream with very first push
git push -u origin local-branch

git push --set-upstream origin <branch>

# checking the url of remotes
git remote -v

# add another url to git
git remote add upstream <url>

# now you can use

git pull upstream master (or other branch names)

upsteam is the standard name used, but you can change it if you want to

$ git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git