Added instructions on how to install using bower

This is a very helpful project. Thanks for sharing!

The README currently does not describe how to install using Bower. If you've used Bower before, it would be pretty easy to figure out how to do a search to see if this project exists on Bower, but I think it would be helpful if the README included explicit instructions for using Bower. (I actually used a different dependency that solves the same problem initially simply because in the other project it was apparent that it was available on Bower.)

Sidenote: There are currently 3 versions of `backbone.routefilter` on Bower, which is why this README says to run `bower install --save git://github.com/boazsender/backbone.routefilter.git#~0.2.0` instead of the customary `bower install --save backbone.routefilter`. I will submit a separate issue for the multiple versions on Bower, but if the multiple versions on Bower is ever resolved, this README should be changed to use the customary install method of `bower install --save backbone.routefilter`.