Placeholder landing page, moved docs page, small fix to header

- Moved the current index page into `/docs/` since we'll be needing `/index.html` for the landing page soon.
- Updated the docs page to make adding new templates easier.
- Small tweaks to decouple the sliding nav styles from the header class so we could use the header without the nav. The funny thing is this was originally needed to fix the weird issue on the current index.html page where it was absolutely positioned partially off the screen. The issue was because there was no nav wrapping it so I wanted to remove the `top` property from `role="header"`. Anyway it's still helpful to have them decoupled.