Update windows installation docs.

Merge branch/doc-updates. 

Updates Windows Installation documentation with correct node.js instructions. 
Update Core Contributor documentation to remove Ruby server information. 

@davideaster Please review, specifically Mac/Linux changes in Core Contributor section. 
I don't think the current branch makes a differences to the fork. Let's switch the link to the top of the repository at `https://github.com/virtual-world-framework/vwf`.