To cite grImport in publications use:

  Paul Murrell (2009). Importing Vector Graphics: The grImport Package
  for R. Journal of Statistical Software, 30(4), 1-37.
  https://doi.org/10.18637/jss.v030.i04.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Importing Vector Graphics: The {grImport} Package for {R}},
    author = {Paul Murrell},
    journal = {Journal of Statistical Software},
    year = {2009},
    volume = {30},
    number = {4},
    pages = {1--37},
    doi = {10.18637/jss.v030.i04},
  }