[pyos][docs] Data sources inaccurate

[sneakers-the-rat]

Part of: pyOpenSci/software-submission#267 (comment)

The README

lists these data sources:

• CrossRef
• Semantic Scholar
• OpenAlex
• PubMed
• dblp
• arXiv
• DataCite
• Zenodo
• Google Books

However I find no mechanism in the code for these:

• OpenAlex
• dblp