To cite package ‘suppdata’ in publications use:

  Pearse, W.D., & Chamberlain, S. (2018). Suppdata: Downloading
  Supplementary Data from Published Manuscripts. Journal of Open Source
  Software, 3(25), 721, https://doi.org/10.21105/joss.00721.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Suppdata: Downloading Supplementary Data from Published Manuscripts},
    author = {{W. D. Pearse} and {S. Chamberlain}},
    journal = {Journal of Open Source Software},
    year = {2018},
    pages = {721},
    volume = {3},
    number = {25},
    doi = {10.21105/joss.00721},
  }