Add grunt task options to README

I've updated the docs with a link to the [grunt-blanket-qunit repo](https://github.com/ModelN/grunt-blanket-qunit), as well as a [blog walkthrough](http://www.geekdave.com/2013/07/20/code-coverage-enforcement-for-qunit-using-grunt-and-blanket/) I created the other day.  We had discussed adding this in https://github.com/alex-seville/blanket/issues/288#issuecomment-18372448

We've been using grunt-blanket-qunit internally at my company for two large projects, and it's working well.  Additionally I am using it with TravisCI for one of my Backbone plugins here: https://travis-ci.org/ModelN/backbone.geppetto

Feedback is most welcome.