Added bibtex file containing the up-to-date working sample of the Zotero
library to data/intermediate. It can be used to count sources based on
their keywords such as how many were sorted out during which step,
which regions they belong to and so on.
Since we now have a 'documentation' directory instead of a
'supplementary-data' one, actual supplementary data should
move to the actual data directory, which is what it does
with this commit.
