Yarn, NodeJS and documentation improvements ### Backends - Support for Yarn (#13, !15) - Support for NodeJS (#12, !17, !18) ### Documentation - Added an example screenshot in the README (#7, !8) - Added a tutorial on how to create your own package manager (!7) ### Build and deployment - Base the project on OpenSavvy Playground (#4, !4) ### Contributions Thanks @intincrab1 for contributing the NodeJS backend!