# Clone your fork
git clone git@github.com:YOUR-USERNAME/YOUR-FORKED-REPO.git

# Add remote from original repository in your forked repository
cd into/cloned/fork-repo
git remote add upstream git://github.com/ORIGINAL-DEV-USERNAME/REPO-YOU-FORKED-FROM.git
git fetch upstream

# Update your frk from original repo to keep up with their changes
git pull upstream master