Update setup instructions to work on a fresh install

I installed node for the first time in this machine and couldn't run the server (or tests) with the commands provided in the README, because it supposes some binaries are available globally.

* Removed `brunch` from the list of required tools (apparently listing `grunt-brunch` in the `package.json` is enough, also I read in issue #2 it's getting removed anyway).
* Added instructions to run the binaries that are installed within the `node_modules` directory.