Minor updates to the Node and CoffeeScript docs

If you use just do `npm install -g jasmine-node`, most setups these days will bark at you and tell you don't have permissions. So, I added some instructions to guide the user if that happens.

I added some information for any Linux users who don't already know how to install Node.js (it turns out there is a `node` package in most package managers that has something to do with amateur radio or something). These days, the official installer updates your `PATH`, so the user *theoretically* shouldn't have to worry about it.