The prerequisites that are required for installing the JupyterLab GitHub extension are as follows:

• JupyterLab 1.0
• A GitHub account for serverextension

The JupyterLab GitHub extension has both a serverextension variable and a labextension variable. I recommend installing both so that you're not rate-limited. The purpose of the serverextension variable is to add GitHub credentials that you will need to acquire from https://github.com/settings/developers and then to proxy your request to GitHub.