The GitHub repository is a drat repository hosting the fivethirtyeightdata package, that is unable to be hosted on CRAN due to its large size. It is meant to be used along with fivethirtyeight package for the full suite of datasets.
Here is a set a vignettes by Dirk Eddelbuettel, the drat package author:
- Drat FAQ,
- Drat for Package Authors,
- Drat for Package Users
- Why Drat?
- Drat Lightning Talk at useR!2015
The drat package page has a longer tutorial, and the blog section on drat has even more.