docs: document external neighbor list #4324

Job	Run time
Build source distribution	23s
determine-arm64-runner	1s
Build wheels for cp311-manylinux_x86_64	5m 15s
Build wheels for cp311-manylinux_x86_64	5m 21s
Build wheels for cp311-macosx_x86_64	8m 3s
Build wheels for cp311-macosx_arm64	5m 26s
Build wheels for cp311-win_amd64	7m 25s
Build wheels for cp310-manylinux_aarch64	4m 30s
build_pypi_index	10s
build_docker (12)	2m 35s
build_docker (_cu11, 11)	2m 55s
upload_pypi	0s
deploy_pypi_index	0s
Pass testing build wheels	2s
	42m 6s

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