Add new section Data Repositories

[LuciMoore]

Add a link to this spreadhsheet: Data Repositories Info spreadsheet and/or add the information from this spreadsheet to the Brain

The spreadsheet is incomplete, so I haven't shared it widely yet, but I think it might be good to go ahead and share it anyway so that folks have access to the information that has already been compiled at least

We could also include a note that this spreadsheet is under construction and invite people to add additional details

Closing out this issue for now as it will be resolved with this update: #225