Clarify documentation for `org-bibtex` bibliography.

[ghost]

The README file has the following passage:

Org-bibtex users can also specify org-mode bibliography files, in which case it will be assumed that a BibTeX file exists with the same name and extension bib instead of org. If the bib file has a different name, use a cons cell ("orgfile.org" . “bibfile.bib") instead

What is an "org-mode bibliography file"? As far as I remember, org's default oc.el supports biblatex, and csl's json as bibliography sources.

Am I even understanging correctly that org-bibtex is what now is called ol-bibtex? So the user is expected to regularly synchronise orgfile.org <-> bibfile.bib by running org-bibtex?

[tmalsburg]

I'm not using org-bibtex myself, but I think it's this: https://gewhere.github.io/org-bibtex

[ghost]

But what does having two files in bibtex-completion-bibliography do?

(setq bibtex-completion-bibliography
      '(("/path/to/org-bibtex-file2.org" . "/path/to/bibtex-file.bib")))

[tmalsburg]

Good question, gotta confess I forget and would have to read the code again. I think we parse the bib file because that's faster but the org file is the source of truth that we edit (the bib file, to my knowledge, is generated from the org file).