Grunt Brand guide

@cowboy Here's the layout for the Brand Guide. You can start editing the content.

@vladikoff I have [another branch](https://github.com/isaacdurazo/gruntjs.com/tree/44-brand-guide)  under gruntjs.com for the assets and the styles needed for this page. I probably should wait to submit a PR, right?
no space in `![ ]` => `![]`