Updated README installation instructions

The installation instructions now reflect the exact process needed to set up ``acorn-player`` from a fresh install. The changes include:

1. Specifying that only Node v0.8.16 has been tested to work and v0.10.4 is confirmed unsupported.
2. Including instructions to symlink in Closure.jar and Grunt.js
3. How to initialize closure git submodule
4. How to run local version of Grunt because ``npm install`` installs Grunt into node_modules

I just re-installed acorn-player using the above changes and everything works!