Create a Research & References assets library

[daveluo]

We're starting to amass quite a lot of informative research papers, how-to and data processing documentation, figures, news articles, and other assets. They're currently scattered around within github issues and comments, gitter, markdown cells within notebooks, etc.

We should create some structure for storing, organizing, and briefly annotating these assets so that they're more easily discovered, referenced, and accessed by contributors actively working on the data. This structure would also serve to guide data product consumers who want to traceback the methodology, research, and data sources behind any part of our work.

For now, this could take the form of a dedicated folder in the repo with its own README containing some guidance for contributors on how to add new assets and storage of files directly there if small enough or pointers in the documentation to where they live online (dropbox, pubmed, arXiv, etc).

In this library, we could also consider saving our own copy of data inputs we use (i.e. HCRIS 2018 cost report zip archives, US census data) in case they're no longer available at their original links or get updated.