add link to Sparkshot.io (#511)
add link to Sparkshot.io (#511)

Sparkshot.io is an art platform for the Lightning Network. Pixels
are revealed in real-time response to micropayments. The artist earns
the proceeds, minus a platform fee.
jlopp/lopp.net,jlopp/lopp.net,jlopp/lopp.net,jlopp/lopp.net