Suggest to add ISC or MIT License here. Thanks for this cool work!

Hi Tom Just to let you know, I've resumed working on my `ggCheysson` package for R, https://friendly.github.io/ggCheysson/index.html I cite you in several places, CRAN URL checks flagged these as "possibly invalid". Had to replace these: * The Tom Shanley Observable notebook citation (`R/data.R`, `R/palettes.R`, `README.md`) previously linked directly to `observablehq.com`, which returns HTTP 429 to automated, non-browser requests and was flagged as a possibly-invalid URL. Replaced with a Wayback Machine snapshot of the same page, which resolves reliably; no more URL NOTE. In `ggplot2` I'm still not able to easily combine color & patterns into a "palette", but that will be next, once the pkg is accepted on CRAN