docs: add document equations for `se_atten_v2` #7908

Job	Run time
Build source distribution	25s
determine-arm64-runner	1s
Build wheels for cp311-manylinux_x86_64	5m 33s
Build wheels for cp311-manylinux_x86_64	8m 22s
Build wheels for cp311-macosx_x86_64	6m 10s
Build wheels for cp311-macosx_arm64	3m 12s
Build wheels for cp311-win_amd64	5m 43s
Build wheels for cp310-manylinux_aarch64	6m 1s
build_docker (12)	2m 22s
build_pypi_index	7s
build_docker (_cu11, 11)	3m 28s
upload_pypi	0s
deploy_pypi_index	0s
Pass testing build wheels	2s
	41m 26s

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