This is the live website. Pushing to the github repo will result in a hook being run that will make the latest version of the master branch go LIVE at http://nova-labs.org. Be warned!
Actually, you probably don't want to push to master, even if you have permissions to. Instead, make a topic branch and submit a Pull Request and get at least one other person to sanity-check your changes and then merge your Pull Request.
Github as some docs on how to use pull requests - you can use either the 'Fork and Pull' or 'Shared Repository' development models, as appropriate to your permission level in the repo.
If you have questions or issues with git, you can ask pj or check out Github's excellent help articles.