Update typings installation in the quickstart

[alexeagle]

We should direct users to get typings from https://www.npmjs.com/~types and stop using typings altogether.

Note that our current instructions are out-of-date: angular/angular#8754

[Foxandxss]

That is on the works, but is not available right now because there are some blocking issues with @types (that doesn't affect the core but affect us).

If you don't mind, I am going to close this and continue at #1872