Better "Getting Started" experience

[romaingweb]

We've had a number of complaints about the new homepage, from people who just want to know how to install / get started with Cucumber but can't see where to go. Also, "download" is the most frequently used search-term on the site.

We need build at least one page of really good "getting started" content, and clearly signpost it from the homepage.

• @romaingweb draft a design for the new homepage section
• Implement the new homepage section
• Provide a great page of documentation to link into