Fix broken link in README
Fix broken link in README

Fixes #139
geofffranks/spruce,geofffranks/spruce,geofffranks/spruce,HeavyWombat/spruce,thomasmmitchell/spruce,jszroberto/spruce,jszroberto/spruce,HeavyWombat/spruce,jszroberto/spruce,thomasmmitchell/spruce,thomasmmitchell/spruce,HeavyWombat/spruce