To cite package 'Observation' in publications use:

  Paul R. Hibbing (2018). Observation: Collect and Process Physical
  Activity Direct Observation Data. URL
  https://github.com/paulhibbing/Observation/.

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {Observation: Collect and Process Physical Activity Direct Observation Data},
    author = {Paul R. Hibbing},
    year = {2018},
    url = {https://github.com/paulhibbing/Observation/},
  }