Update template to modern Carp idioms

[carpentry-agent]

Addresses #1.

• Module-level docs: added a (doc MyMod ...) block with installation/usage examples, matching the pattern used by carpentry-org packages like strbuf, json, and http.
• docs-url config: added (Project.config "docs-url" ...) to gendocs.carp so generated docs link back to the repository.
• File naming guidance: updated README to tell users to rename main.carp to match their module name (e.g. my-mod.carp for MyMod), and to update load paths in gendocs.carp and test/tests.carp accordingly. Also reminds users to set docs-url.

---

Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet.

[carpentry-agent]

Build & Tests

CI passing on both ubuntu and macOS. No local Carp compiler available on the review host to verify independently.

Findings

1. Setup instructions in module doc string (main.carp:1-16). The (doc MyMod ...) block mixes API documentation ("is a template module you should replace with your own") with project setup instructions ("Rename this file to match your module name"). Module doc strings end up in generated documentation — a user browsing the docs would see instructions meant for the library author. Consider moving the rename/setup guidance to a comment above the doc form, and keeping the doc string focused on what the module does.

2. Gratuitous reformatting of greet (main.carp:19). The multi-line if was collapsed to a single line. For a template repo that beginners will read and modify, the multi-line form was arguably clearer. This is minor but it's a change with no upside for the template's purpose.

3. Good additions. The docs-url config in gendocs.carp, the README guidance on renaming main.carp and updating load paths, and the overall modernization are all useful. The README is noticeably better.

Verdict: merge

The substantive changes (docs-url, README guidance, module docs) are improvements. The style nits above are minor and not blocking.