git add remote upstream

applejack:single_cell_segmentation hqin$ git remote -v 

origin https://github.com/QinLab/single_cell_segmentation.git (fetch)

origin https://github.com/QinLab/single_cell_segmentation.git (push)

$ git remote add upstream https://github.com/opnumten/single_cell_segmentation 

applejack:single_cell_segmentation hqin$ git remote -v

origin https://github.com/QinLab/single_cell_segmentation.git (fetch)

origin https://github.com/QinLab/single_cell_segmentation.git (push)

upstream https://github.com/opnumten/single_cell_segmentation (fetch)

upstream https://github.com/opnumten/single_cell_segmentation (push)

~$ git fetch upstream

remote: Counting objects: 9, done.

remote: Total 9 (delta 6), reused 6 (delta 6), pack-reused 3

Unpacking objects: 100% (9/9), done.

From https://github.com/opnumten/single_cell_segmentation

 * [new branch]      master     -> upstream/master

~$ git checkout master

Already on 'master'

Your branch is up-to-date with 'origin/master'.

applejack:single_cell_segmentation hqin$ 

applejack:single_cell_segmentation hqin$ git status

On branch master

Your branch is up-to-date with 'origin/master'.

nothing to commit, working tree clean

Reference:
https://help.github.com/articles/configuring-a-remote-for-a-fork/
https://help.github.com/articles/syncing-a-fork/