Images not accessible in dark theme

[sajayantony]

The readme has images that aren't visible correctly in dark theme. Here is a screenshot.

https://github.com/notaryproject/nv2/blob/prototype-2/README.md

@SteveLasker

[SteveLasker]

ack, I’ll update the background in the next round of content updates.

[sajayantony]

Fixed by #78