butane/docs: add file append and overwrite examples

[JasonColapietro]

Summary

Moved over from coreos/butane#729
at @yasminvalim's suggestion, now that Butane development lives here.

butane/docs/examples.md showed contents but never append or overwrite,
so the difference between the three had to be inferred from the spec. This adds
three examples:

• appending a sudoers rule to the shipped /etc/sudoers, with the safe default
  overwrite: false
• the equivalent /etc/sudoers.d/ drop-in, which is usually preferable since it
  survives updates to the shipped file
• replacing a filesystem node with overwrite: true and ordinary contents

The sudoers examples deliberately allow a single command with exact arguments,
with a note against granting unrestricted passwordless access to shells, package
managers, or container runtimes.

Testing

• each of the three new blocks passes butane --check --strict, using a
  butane binary built from this tree
• ./test — Success, exit 0

One thing worth flagging: ./test here does not validate <!-- butane-config -->
blocks under butane/docs/. The docs validator only walks docs/ looking for
<!-- ignition --> markers, so the Butane YAML in these docs is currently
unchecked — Butane's own ./test validated it before the merge. I checked these
blocks by hand. Glad to open a separate issue or PR to restore that coverage if
you'd like it.

Fixes #2270.

[coderabbitai]

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butane/docs/examples.md (1)

152-181: LGTM!

Also applies to: 183-197

---

📝 Walkthrough

Walkthrough

The documentation adds examples for appending sudoers rules and overwriting an existing filesystem node. The release notes record the file behavior documentation update.

Changes

File behavior documentation

Layer / File(s)	Summary
Document append and overwrite behavior butane/docs/examples.md, docs/release-notes.md	The examples show append with overwrite: false for sudoers files and overwrite: true for replacing /etc/example.conf. The release notes record these examples.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to ae150

This PR adds localized documentation examples and introduces no actionable merge-blocking risk; it is merge-ready after normal checks and review.

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses the required subsystem format, lowercase imperative description, and no trailing period.
Description check	✅ Passed	The description clearly explains the documentation changes, testing, migration context, and linked issue.
Linked Issues check	✅ Passed	The changes satisfy issue #2270 by documenting append behavior with the requested sudoers example and overwrite-related guidance.
Out of Scope Changes check	✅ Passed	All changes support the documented append and overwrite examples requested by issue #2270.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (1 skipped: 1 unsupported.)
Commit Message Convention	✅ Passed	The PR range contains one non-merge commit; its subject is butane/docs: add file append and overwrite examples, with a valid subsystem, lowercase imperative description, and no period.

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Actionable comments posted: 1

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Inline comments:
In `@butane/docs/examples.md`:
- Line 152: Update the documentation example to clarify that contents with
overwrite: false does not replace a pre-existing filesystem node; instruct
readers to set overwrite: true when contents must replace the existing node,
while preserving the distinction between complete-file contents and append
behavior.

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docs/**

⚙️ CodeRabbit configuration file

docs/**: Documentation served via GitHub Pages/Jekyll. Every platform must be documented in supported-platforms.md. The ./test script validates doc consistency.

Files:

• docs/release-notes.md

🔇 Additional comments (3)

butane/docs/examples.md (2)

154-181: LGTM!

---

183-197: LGTM!

docs/release-notes.md (1)

19-19: LGTM!