In the README 'io.js' section, explain what io.js was?

[severo]

The README 'io.js' section only refers to https://github.com/iojs/io.js/ for people to understand what io.js is. But it is now redirected to https://github.com/nodejs/node, so it took me some time to find relevant information about this (and understand I should not worry about io.js anymore).

Maybe add a sentence that gives context, or link to a reference URL like https://medium.com/node-js-javascript/io-js-week-of-may-15th-9ada45bd8a28 or https://en.wikipedia.org/wiki/Node.js#History.