An image for search-engines/facebook

This should close #297? Please let me know what you all think of the image, tag-line, code, etc.
cc. @roryaronson @simonv3 @rickcarlino @emily-plummer and everyone else
Same thing as above:

```
<meta property="og:image" content="<%= image_path("blahblahblah.png")" />
```