Document the bench process

[sylvestre]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[codspeed-hq]

CodSpeed Performance Report

Merging #8809 will degrade performances by 2.75%

_{Comparing sylvestre:perf-doc (8e71117) with main (013a385)}

Summary

❌ 2 regressions
✅ 75 untouched
⏩ 73 skipped¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	du_human_balanced_tree[(5, 4, 10)]	10.1 ms	10.4 ms	-2.75%
❌	du_summarize_balanced_tree[(5, 4, 10)]	8.3 ms	8.5 ms	-2.01%

Footnotes

1. 73 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)