Self-proteome docs advertise nonexistent tissue-source parameters #458

docs/self_proteome.md advertises tissue_source="hpa"/"gtex" and min_expression= for SelfProteome.from_ensembl(include="protected_tissues"), but neither parameter exists. The real contract uses tissues, min_tissue_ntpm and optional caller-supplied tissue_gene_ids.

Correct the public example against the callable, keep expression distinct from presentation, and identify oncoref as CTA membership authority. Found while reviewing #455 / PR #456; include this small documentation correction there.