docs folder and some fuse docs. closes #259

re https://github.com/jbenet/go-ipfs/pull/260, https://github.com/jbenet/go-ipfs/issues/259
> `All data is stored in a leveldb data store in `~/.go-ipfs/datastore`.`

Maybe: 

`All data is stored in a leveldb data store inside $IPFS_DIR (usually ~/.go-ipfs/datastore).` (subject to #394)