Update README for use with compose.io

I was transferring data between databases on https://www.compose.io/ and wanted to share my notes.

* To build `seed` two packages are required `code.google.com/p/log4go` `labix.org/v2/mgo`
* To authenticate with compose.io an `authSource` parameter is required
* More verbose shell script example

Thanks again for this software :+1: