Add notes about BoundingBoxes transform utils in ops/boxes docstrings #2026

Job	Run time
onnx / linux-job	5m 4s
unittests-extended / linux-job	17m 14s
unittests-linux (3.10, linux.12xlarge, cpu) / linux-job	22m 42s
unittests-linux (3.11, linux.12xlarge, cpu) / linux-job	20m 40s
unittests-linux (3.8, linux.12xlarge, cpu) / linux-job	22m 44s
unittests-linux (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job	18m 56s
unittests-linux (3.9, linux.12xlarge, cpu) / linux-job	22m 32s
unittests-macos (3.10, macos-12) / macos-job	1m 40s
unittests-macos (3.11, macos-12) / macos-job	1m 34s
unittests-macos (3.8, macos-12) / macos-job	47m 24s
unittests-macos (3.8, macos-m1-12) / macos-job	31m 10s
unittests-macos (3.9, macos-12) / macos-job	1m 36s
unittests-windows (3.10, windows.4xlarge, cpu) / windows-job	1m 37s
unittests-windows (3.11, windows.4xlarge, cpu) / windows-job	1m 21s
unittests-windows (3.8, windows.4xlarge, cpu) / windows-job	1m 28s
unittests-windows (3.8, windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job	23m 50s
unittests-windows (3.9, windows.4xlarge, cpu) / windows-job	1m 42s
	4h 3m 14s

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