About git-tracker : Integrate Pivotal Tracker into your Git workflow.!
More Information: https://github.com/stevenharman/git_tracker
Steps:

1. Open terminal by pressing command+space, type terminal and hit Enter key.
2. Run

   ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" < /dev/null 2> /dev/null

3. Install

   brew install git-tracker

Done!

More about git-tracker:

GitTracker, or git-tracker, is a Git hook that will scan your current branch name looking for something it recognizes as a Pivotal Tracker story number. If it finds one, it will automagically add it, in the special format, to your commit message