Give better context of this repo

[williamkapke]

This repo is a bit confusing now that so many things have progressed!

I took a stab at updating the README. Tried to Keep It Simple.

Also, if someone could change the repo description-

Maybe just say "A place to discuss the Node.js roadmap"... but I definitely think the url should be removed.

[williamkapke]

@nodejs/roadmap please review.

[fhemberger]

Good catch! Sorry it took so long for this change, PR got buried in GitHub notifications.

I split the repo in two branches instead:

• gh-pages: The old io.js roadmap, still linked on iojs.org.
• master: Just the new README for the Node.js roadmap.

[williamkapke]

Oh wow! An even better solution! 🌟 🎉 Awesome work.