Documentation-o-rama

A first stab at documenting the three projects.  More detail on Kronos than the other projects.  Also some information on contributing, style guide, etc.
Not a problem with the docs, but maybe something to think about later: if there are 3rd party contributors in the future, they will be making pull requests from forked repos and won't be able to push to Locu/kronos/master. I think [this is a pretty good way to do it](https://github.com/edx/edx-platform/wiki/How-to-Rebase-a-Pull-Request) and we might be able to modify push_branch.sh to automate some of that process.