Goal: add documentation to readme reflecting Claude and Codex's use of /goal

## Goal

Our readme should contain references to the use of `/goal` in Claude Code and Codex, with appropriate links. Not extended discussion, but we want to note that we are using this now-standard term.

We also want to make sure we link to https://github.com/githubnext/autoloop which also inspired this repo. Autoloop is a similar goal-driven agentic workflow, with more of an emphasis on scientific exploration.

## Completion Contract

The README.md "Built On" section (or a similar appropriate section) links to:
- Claude Code `/goal` documentation
- Codex `/goal` documentation
- https://github.com/githubnext/autoloop with a brief description

## Evidence / Verification

```bash
set -euo pipefail
grep -q "autoloop" README.md
grep -qi "claude" README.md
grep -qi "codex" README.md
grep -q "https://github.com/githubnext/autoloop" README.md
```

All commands must exit 0.

## Scope and Constraints

Allowed files:
- `README.md`

Do not remove existing content. Keep additions brief — a few lines, not paragraphs.

## Iteration Policy

This is a single-run goal. Read the current README, add the references, and verify.

## Blocked Stop Condition

If the official `/goal` documentation URLs for Claude Code or Codex cannot be found or confirmed, add placeholder references noting the feature and stop with a comment listing which URLs need human confirmation.

まず README.md を読み、"Built On" セクションまたは簡単な参照を記載するのに適した別の場所を見つけてください。Claude Code と Codex /goal の公式ドキュメント URL を確認し、両方のリンクに加えて githubnext/autoloop の短い説明とリンクを追加し、その後 issue にある 4 つの grep コマンドを実行して完了を確認してください。

索引モデルが issue の本文から書いたものです。