gistfile1.sh

git remote add upstream [Clone Url]
git fetch upstream
git checkout master

## At this point, you have two options:

git merge upstream/master   # Merge yours and theirs
git push origin master     # Push back to your fork

git reset --hard upstream/master    # Make yours look *exactly* like theirs, lose your changes;
git push --force origin master     # Only use this if nobody uses your fork!