github: this branch is N commits behind
Don't try it with the github site (it's possible but a bad idea). Instead use the "clean" way and do this from inside the dir with your git-repo:
Tell your repository about the original one:
git remote add upstream git://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git
Get the original branches:
git fetch upstream
Pull in the original data in to your branch:
git pull upstream master
Push this to your github repository:
git push
Update: you can now perform this action via the GitHub frontend's Fetch Upstream
button - see the Release Notes here:
You can now use the web UI to synchronize an out of date branch of a fork with its upstream branch. If there are no merge conflicts between the branches, the fork's branch is updated either by fast-forwarding or by merging from the upstream's branch. If there are conflicts, you will be prompted to open a pull request to resolve.
Old Answer:
Create a pull request that merges OtherOne:master
into your forked repo, then merge it. That should remove the message and ensure that the two repos are indeed synchronized.