This page gives me useless information:
$ git checkout -b upstream/master
$ git remote add upstream git://github.com/upstream_maintainer/master.git
$ git pull upstream remote
$ git checkout master
$ git merge upstream/master
If you do that, it frankly doesn't work. Why? "upstream/master" etc. all have special meanings.
Here's the real process & explanation (thanks to Erik Tollerud for some help):
git checkout master # (assuming you have a local branch named master - otherwise, pick whatever branch you want synced)
git remote add original git@github.com:thing/thing.git # "upstream" = "original" = "remote" - the place you're trying to sync from
git fetch original # 'original' being the name YOU gave for the "remote/original" repository
git merge master original/master # now merge the "original/master" branch (they should have a branch named "master" too, otherwise you have to figure out which branch to get) into your master
git push # push your now-merged stuff back to github
# I was instructed to use these commands. They didn't work.
# git reset original # the word "original" here matches the word "original" on the previous line
# git reset --hard original # this will overwrite local changes
