To cite package 'nppbib' in publications use:

  David Allingham and D.J. Best (2020). nppbib: Nonparametric Analysis
  of Partially-Balanced Incomplete Block Designs. R package version
  1.2-0.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {nppbib: Nonparametric Analysis of Partially-Balanced Incomplete Block Designs},
    author = {David Allingham and D.J. Best},
    year = {2020},
    note = {R package version 1.2-0},
  }