Added ROADMAP.md

@izs this is more of a gesture than an actual pull-request: put this where-ever you see fit. There were a few folks on other parts of the Internet that were asking for more visibility and since the roadmap we discussed over the summer for this post:

http://blog.nodejitsu.com/npm-innovation-through-modularity

was approved by you I saw no problem duplicating the copy in the repository to make it more accessible. 

cc/ @maxogden @rvagg @domenic @luk @jden