docs: document the new option #1344

Job	Run time
ash-ci / mix deps.get	14s
ash-ci / mix igniter.upgrade	4s
ash-ci / audit	2m 26s
ash-ci / MIX_ENV=test mix.compile	2m 29s
ash-ci / mix credo --strict	42s
ash-ci / mix docs	2m 10s
ash-ci / MIX_ENV=dev mix.compile	2m 21s
ash-ci / mix ash.codegen --check	0s
ash-ci / mix dialyzer	5m 51s
ash-ci / mix format --check-formatted	42s
ash-ci / mix sobelow	41s
ash-ci / mix spark.cheat_sheets --check	39s
ash-ci / mix test	1m 9s
ash-ci / mix spark.formatter --check	41s
ash-ci / mix deps.unlock --check-unused	41s
ash-ci / Deploy docs to GitHub pages.	8s
ash-ci / NIF ${{ matrix.nif }} - ${{ matrix.job.target }} (${{ matrix.job.os }})	0s
ash-ci / Release	0s
	20m 58s

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