git-behind
Tells you if your branch is behind and needs to pull/merge
ecker00 223 1 0.2.0 MIT GitHub

Atom: Git Behind

Want to be reminded of the latest changes your team is doing?

Git Behind will tell you when your local branch falls behind the origin/master branch or any origin branch you specify.

screenshot

In the simplest terms, this package runs the command git fetch -v --dry-run every few minutes and looks if the specified branch is [up to date] or not.