[contributing]: {{ site.github.repository_url }}/blob/gh-pages/CONTRIBUTING.md
[cran-checkpoint]: https://cran.r-project.org/web/packages/checkpoint/index.html
[cran-knitr]: https://cran.r-project.org/web/packages/knitr/index.html
[contributing]: {{ site.github.repository_url }}/blob/gh-pages/CONTRIBUTING.md
[cran-checkpoint]: https://cran.r-project.org/web/packages/checkpoint/index.html
[cran-knitr]: https://cran.r-project.org/web/packages/knitr/index.html