docs: Provide more info on custom state attributes #206

Job	Run time
ash-ci / audit	41s
ash-ci / mix deps.get	16s
ash-ci / mix igniter.upgrade	4s
ash-ci / MIX_ENV=test mix.compile	25s
ash-ci / mix docs	33s
ash-ci / mix credo --strict	28s
ash-ci / mix ash.codegen --check	0s
ash-ci / MIX_ENV=dev mix.compile	24s
ash-ci / mix dialyzer	3m 18s
ash-ci / Deploy docs to GitHub pages.	0s
ash-ci / mix format --check-formatted	28s
ash-ci / mix sobelow	21s
ash-ci / mix spark.cheat_sheets --check	18s
ash-ci / mix spark.formatter --check	22s
ash-ci / mix test	58s
ash-ci / mix deps.unlock --check-unused	23s
ash-ci / Release	0s
	8m 59s

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