To cite package ‘postcards’ in publications use:

  Kross S (2024). _postcards: Create Beautiful, Simple Personal
  Websites_. R package version 0.2.3,
  <https://github.com/seankross/postcards>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {postcards: Create Beautiful, Simple Personal Websites},
    author = {Sean Kross},
    year = {2024},
    note = {R package version 0.2.3},
    url = {https://github.com/seankross/postcards},
  }