Updated CONTRIBUTING.md, thanks to @vlee489 for point out broken links.
Updated CONTRIBUTING.md, thanks to @vlee489 for point out broken links.

PiNet/PiNet.github.io,PiNet/PiNet.github.io,vlee489/PiNet.github.io,vlee489/PiNet.github.io,vlee489/PiNet.github.io,PiNet/PiNet.github.io,PiNet/PiNet.github.io