add lionel radisson's pen plotter observable notebooks

README.md

@@ -133,6 +133,7 @@ Tools to create vector artwork from scratch or by conversion from other formats.
 - [Maker.js](https://maker.js.org) - Library for creating 2D vector drawings for CNC and laser cutter machines.
 - [Turtletoy](https://turtletoy.net) - Browser-based JavaScript turtle graphics API with SVG export.
 - [cozyvec](https://github.com/brubsby/cozyvec) - Web/Standalone terminal environment for plotter art and tweet plots.
+- [makio135/plotter](https://observablehq.com/collection/@makio135/plotter) - An [Observable](https://observablehq.com/) notebook collection full of plotter-oriented work.
 
 ### Vector Utilities