To cite hockeystick in publications use:

  Hernando Cortina. hockeystick: Download and Visualize Essential
  Climate Change Data (2020)

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {hockeystick: Download and Visualize Essential Climate Change Data},
    author = {Hernando Cortina},
    year = {2020},
    url = {https://cortinah.github.io/hockeystick/},
  }