The Tracker API supports integration with post-commit hooks of Source Control Management (SCM) systems such as Subversion, Git/GitHub, etc. When a commit is made to the SCM, a trigger can call the Tracker API to add a story comment with the commit ID, author, and message. It can also optionally change story state.
For all the details, including commit syntax and instructions on how to enable SCM integration, please see the API Help page.
GitHub offers a service hook for Pivotal Tracker, which makes it easy to link your commits to Tracker stories. For more please see GitHub’s service hook for Tracker.