### Task B5: Document the feature in the README

**Files:**
- Modify: `README.md`

**Interfaces:**
- Produces: a short "Patching packages" section explaining the registry and linking the design spec.

- [ ] **Step 1: Add a README section**

Add a `## Patching packages` section after the "Build Process" section describing: why patching exists (compiler/OS-specific failures cascading via shared deps like RcppParallel), where the registry lives (`local/patches/registry.json`), the two tiers (env/configure/Makevars overrides vs source diffs), and that bincraft pre-builds patched binaries served to pak. Link `specs/2026-06-30-package-patching-design.md`.

- [ ] **Step 2: Commit**

```bash
git add README.md
git commit -m "docs(patches): document the package patching workflow"
```

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