Document source of various metadata files

[steven-sheehy]

The cht, dat, and metadat folders contain files whose source of truth is unclear. Without knowing the source, it's hard to know if the data needs to be updated. Also, if the source is known then automatic processes could be developed to automatically keep them up to date or alternative sources could be suggested. For example, it might be interesting to replace most of the metadat files with code that scrapes a game database like screenscraper.fr or thegamesdb.net.

This documentation could be in the form of a simple README inside each specific sub-folder or a comment with a URL added to the header of the dat file.