Do this once:
$ git remote add upstream git@github.com:armmbed/mbed-os.git
And do this when need to sync:
$ git fetch upstream
$ git merge upstream/master
$ git push
Do this once:
$ git remote add upstream git@github.com:armmbed/mbed-os.git
And do this when need to sync:
$ git fetch upstream
$ git merge upstream/master
$ git push