You're an academic, sitting on the shoulder of giants, and small regular folks who worked hard. Cite their work!
In your references, you will need to cite (thank) the R team, as well as any package authors for packages that you used.
Cite R:
R Core Team (2013). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL http://www.R-project.org/.
Ask R how the package authors want to be cited by asking R:
To cite the R package 'cluster' in publications use:
> citation(package = "cluster") Maechler, M., Rousseeuw, P., Struyf, A., Hubert, M., Hornik, K.(2013). cluster: Cluster Analysis Basics and Extensions. R package version 1.14.4.