Improve instructions/make a curriculum page

[max-mapper]

@lyle @tmpvar @brycebaril @darkroastruth I did a first pass at Export > Orthogami and Export > Paperstack in the app, try it out on http://voxelbuilder.com/

I think we need better instructions though, ideally a sort of guide that is targeted at people who want to use this in classroom settings

Some stuff to work on if anyone wants to help w/ this issue

• improve front page copy (index.html)
• improve pop-up instructions that come up the first time you launch the builder (edit.html)
• add instructions to the Export Orthogami and Export Paperstack modals (edit.html)
• if it makes sense make a whole new page that is an end-to-end guide