Document structure of results tarball

[chuckha]

We should have strict rules about how data in a results tarball is arranged, so that ingesting sonobuoy results can be done in an automated way without lots of if statements and special casing.

We can start with simple documentation, outlining the paths within the tarball and what should be contained in them, etc.

[jesscodez]

This is pretty much addressed by #43 (note that some sections are still proposals, but it's a decent overview)