Refactor index page

[mbaudis]

The index page is a bit overloaded with info that is/should be represented mainly in docs.genomebeacons.org. I suggest making this very general (especially about framework/models) and point to the documentation site. Otherwise a bit confusing & inviting version drift ...

[laurenfromont]

I would like to give this to our new dissemination officer. She's not familiar with Markdown so we'll leave it a bit more time, but it's an easy exercise to prepare for future documentation updates.