Managing dependencies: use broccoli-static-compiler

Explain how to edit Brocfile.js and use broccoli-static-compiler to copy parts of a bower dependency.

I was missing this information, and managed to get it working:
https://stackoverflow.com/questions/23871749/ember-cli-is-there-a-way-to-copy-a-vendor-directory-to-public-assets
Merge pull request #821 from jdhoek/patch-1

Managing dependencies: use broccoli-static-compiler