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. 


If we keep this content (see comment on Line 116 above), instead of featuring one polyfill and having a link to a page listing all polyfills, why not list all polyfills here?