Create code example that scales about ggsci HOT 1 CLOSED

By switching to pngquant (lossy compression) in 44a8ce1, I was able to achieve 30Kb per file using dpi=72 and fig.retina=2 with ragg::agg_png. The README outputs and vignette outputs are ~900Kb each now.

Package builds and checks ok even if pngquant is not installed (just with much larger built vignette size).

The only thing to remember is to have pngquant installed on the R CMD build machine when submitting to CRAN.

I'd say this solution would scale well - closing this for now.

from ggsci.