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.
Tracker includes a GitHub integration, which makes it easy to connect stories and epics to git commits, pull requests, and branches. See GitHub Integration for more detail.