Add a wiki page on contributing project pages

A comprehensive guide on submitting project pages using pull requests.
"you have to move the source to a new branch":  You aren't really moving it, your are just creating a new branch. Just say "you need to create a new branch called `gh-pages`. You should also explain that this lets your preview the whole website with your changes (different from the markdown preview that shows when viewing the individual files).

`gh-pages` does not need double quotes in addition to the code formatting.