New Getting Started page

@thomasgohard 
Here is the new Getting Started along with edits I made based on some of Paul's comments in the old pull request. I also edited the background for the breadcrumbs which I forgot to do in the menu-footer-colours pull request. Now the background is white to follow with the rest of the white background of the site. 


Why are we talking about the polyfills here? A polyfill is not something that people choose to add to their pages. A polyfill just adds missing support for an HTML5 feature in browsers that don't yet support it.

Unless we want to highlight HTML5 features that we make safe to use. But then I wouldn't present it in terms of polyfills but in terms of HTML5 features.