Update todo list

Removed the 'Open source' item from the todo list.

Author: grega

README.md

@@ -2,7 +2,6 @@
 
 Todo:
 - Set up automated testing and publishing through GitHub Actions
-- Open source
 
 A small, runtime-agnostic, library that explains Python error messages in a friendlier way, inspired by [p5.js's Friendly Error System](https://p5js.org/contribute/friendly_error_system/).