Makes a stab at improving this repositories documentation

I think the lead is you, David, as you've made most of the IATI commits. I listed you as "owner" on the [Asset Register](https://docs.google.com/spreadsheet/ccc?key=0Ah9lTxggD0MbdDAwOU94VFppT2JUM0loVWxzbjVEaGc&usp=drive_web#gid=0), and have submitted any changes I've made as pull requests to be approved by you.