Produce user documentation

[gubuntu]

The realtime system needs user documentation.

• Public front-end overview and help
• realtime-specific information that is not in inasafe docs
• how to use the site, upload ash etc.
• links to inasafe docs
• links to training materails

To be published on a realtime Django/GeoNode instance

[gubuntu]

use flatpages implemented in #70 and avoid repeating About content

or add to inasage.org (where realtime 'for users' points)