Sync a fork of a repository to keep it up-to-date with the upstream repository. https://help.github.com/articles/syncing-a-fork/
git fetch upstream
git checkout master
git merge upstream/master
git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git
https://help.github.com/articles/resolving-a-merge-conflict-from-the-command-line/