Changes the PiNet documentation link.

[vlee489]

change all https://github.com/PiNet/PiNet-Documentation to
https://github.com/PiNet/PiNet.github.io

As https://github.com/PiNet/PiNet-Documentation leads to a 404.

[gbaman]

Thanks @vlee489, but your Atom editor is set up slightly wrong so is removing trailing whitespace which is kind of important for markdown. I have added your changes and included instructions on how do disable the Atom feature.
f648895