Add user types document

This is an initial start for the various types of users who will be interacting with our system. This is not an exhaustive list, nor is any user fully documented. Most of the information was pulled from the Challenge Post listing.

The intention of this document is to have a place to start defining our users.
differentiate civilians into reports and non-reporters
change word wrapping to line breaks
Merge pull request #16 from vtsatskin/user-types

Add user types document