docs: document external neighbor list (#3056) #4331

Job	Run time
Build source distribution	22s
determine-arm64-runner	1s
Build wheels for cp311-manylinux_x86_64	5m 15s
Build wheels for cp311-manylinux_x86_64	5m 11s
Build wheels for cp311-macosx_x86_64	11m 56s
Build wheels for cp311-macosx_arm64	5m 50s
Build wheels for cp311-win_amd64	5m 47s
Build wheels for cp310-manylinux_aarch64	4m 30s
build_pypi_index	15s
build_docker (12)	7m 6s
build_docker (_cu11, 11)	8m 33s
upload_pypi	0s
deploy_pypi_index	9s
Pass testing build wheels	2s
	54m 57s

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