docs: mark repo deprecated; point to trunk-io/docs2

[samgutentag]

Summary

Adds a deprecation banner at the top of the README pointing to trunk-io/docs2 (Mintlify), which is now the active documentation source for docs.trunk.io.

Stopgap until a GitHub admin can archive this repo fully. All outstanding PRs have already been closed (audit completed 2026-05-20).

Test plan

• Banner renders as a blockquote at the top of the rendered README on github.com.

[trunk-staging-io]

😎 Merged successfully - details.

[claude]

Claude finished @samgutentag's task in 50s —— View job

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PR Review

• Read PR diff and README
• Check for typos, grammar, formatting
• Check documentation consistency
• Post review

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Summary

The deprecation banner is clear, well-placed, and accurately points users to trunk-io/docs2. As a stopgap before archival, this does its job. Nothing blocking.

Findings

Banner (line 1) — Reads well. The em dash, the GitBook-era framing, and the "New PRs against this repo will not be merged" closer all land cleanly.

Bonus cleanup (line 42) — The diff also quietly replaces a U+202F NARROW NO-BREAK SPACE with a regular space in the screenshot alt text ("32 AM"). Nice incidental fix, even though it's not called out in the description.

Optional nits (non-blocking)

1. Contributing section contradicts the banner. Lines 38–40 still invite users to "fork the repo and open a PR with your changes." Given the banner explicitly says new PRs won't be merged, a future pass could redirect contributors to trunk-io/docs2. Not worth holding this PR for — once the repo is archived, the point is moot.

2. "Local Development" section describes the GitBook sync workflow as if it's live. Same story: stale once archived, but worth a note if archival slips.

3. Filename casing — the file is readme.md (lowercase) rather than the conventional README.md. Pre-existing, not introduced here, but worth flagging since GitHub still surfaces it fine and renaming now would just add noise on a soon-to-be-archived repo.

Verdict

LGTM as a stopgap. Ship it.
• Branch: sam-gutentag/deprecate-readme

[github-actions]

Auto-approved: Claude code review passed.