REPO_POLICIES: name examples/ in README, correct the lint example's link

As #159 (comment) says.

- `README.md`: Design names `examples/`.
- `prompts/REPO_POLICIES.md`: the sentence linking
  `examples/go-lint-system-libraries.Dockerfile` says the file holds the
  first lines of a lint phase.

Model: opus-5-5

README.md

@@ -175,7 +175,8 @@ share, and evolve prompts across projects.
 The repository is a collection of Markdown files organized in the `prompts/`
 subdirectory. Each file contains one or more related prompts or policy
 documents. There is no build step or runtime component; the prompts are consumed
-by copying them into other projects or referencing them directly.
+by copying them into other projects or referencing them directly. `examples/`
+holds the example `Dockerfile` files that `prompts/REPO_POLICIES.md` links to.
 
 ## Template Repos