l10n: docs: add update PO instructions in AGENTS.md
Add a new section to po/AGENTS.md to provide clear instructions for updating language-specific PO files. The improved documentation significantly reduces both conversation turns and execution time. Performance evaluation with the Qwen model: # Before: instructions in po/README.md; the custom prompt # references po/README.md during execution git-po-helper agent-test --runs=5 --agent=qwen update-po \ --prompt="Update po/zh_CN.po according to po/README.md" # After: instructions in po/AGENTS.md; the built-in prompt # references po/AGENTS.md during execution git-po-helper agent-test --runs=5 --agent=qwen update-po Benchmark results (5-run average): | Metric | Before | After | Improvement | |-------------|---------|--------|-------------| | Turns | 22 | 4 | -82% | | Exec. time | 38s | 9s | -76% | | Turn range | 17-39 | 3-9 | | | Time range | 25s-68s | 7s-14s | | Signed-off-by: Jiang Xin <worldhello.net@gmail.com>