Add cloud instructions

[arduino5144]

I think it would be a good idea to add instructions on how to set up cloud variables in your own instance. This would be a very useful wiki page to me, and anyone else making a scratch fork.

[RIT-entertainment]

If you want to save projects to the server, then config storage.js and save-project-to-server.js

[RIT-entertainment]

If you are using scratch-www, then follow This Guide