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. 


Having the border only on the `<summary>` element creates a visual disconnect once the `<details>` element is expanded as the summary is boxed separately from it's details.