docs/README.md documentation map omits doctor-findings.md

[codeforester]

Problem

docs/README.md is the canonical map of all documentation in the docs/ directory. It lists every document under "Core Documents" and "Feature And Boundary Documents" — but doctor-findings.md is missing entirely.

doctor-findings.md is one of the most externally useful references in the repository. It documents every stable BASE-D*, BASE-P*, and BASE-H* finding identifier so teams can build automation, suppression policies, and runbooks against basectl doctor --format json. Omitting it from the docs map means contributors and adopters will not discover it through the documentation index.

Fix

Add doctor-findings.md to the "Feature And Boundary Documents" section of docs/README.md:

- [Doctor Finding IDs](doctor-findings.md) is the stable reference for `BASE-D*`,
  `BASE-P*`, and `BASE-H*` finding identifiers used by `basectl doctor --format json`.

Also add a link from docs/README.md to doctor-findings.md in the main README's Documentation section, since it is directly relevant to the basectl doctor description.