Add user documentation

[countvajhula]

In addition to the basic mechanics of setting things up and running various scripts that will be in the README, we also need general user documentation that describes the overall process of DIA, how to do it, any learnings from Qi DIA or other instances of DIA that haven't been captured elsewhere, etc. that will be useful to DIA participants and help us be more effective and efficient.

As a start, we should move the DIA.scrbl file here from the foundation repo, since this file describes a specific process that we are following to do DIA now. The general ideas and goals are already captured in the Attribution_Model document and that is more appropriate in the foundation repo.

[countvajhula]

I've moved the DIA scribble file to this repo from the foundation repo (hosted on github pages and built via CI). We still need to add the learnings and other tips from previous instances of conducting DIA and generally flesh out the user docs.