ggplot2 footnote

labs(caption = "my caption") adds a footnote:

ggplot(mtcars, aes(mpg, wt, colour = cyl)) + 
  geom_point() + 
  labs(caption = "(Pauloo, et al. 2017)")

I would use something like that:

pdf("filename.pdf", width=10, height=6) # open an appropriate graphics device
print(p)
makeFootnote() # from webpage above (uses grid.text; ggplot2 is based on grid)
dev.off()