Update landing page copy

[Robinlovelace]

To mention the NPT and other key features of the NPW:

• That it can be used to share design
• Key metrics

[Robinlovelace]

I've had a bash in #96.

The previous version linked to the NPT but did not mention the relationship between the NPT and NPW. That content could be elsewhere. I also tried to mention other key features of the NPW.

[dabreegster]

Fixed in the new repo