docs: document use of compound types with AshPhoenix.Form (#273) #1067

Job	Run time
ash-ci / mix deps.get	23s
ash-ci / mix igniter.upgrade	6s
ash-ci / audit	53s
ash-ci / MIX_ENV=test mix.compile	30s
ash-ci / MIX_ENV=dev mix.compile	31s
ash-ci / mix credo --strict	3s
ash-ci / mix docs	28s
ash-ci / mix ash.codegen --check	0s
ash-ci / Deploy docs to GitHub pages.	3s
ash-ci / mix dialyzer	3m 50s
ash-ci / mix format --check-formatted	32s
ash-ci / mix sobelow	34s
ash-ci / mix spark.cheat_sheets --check	30s
ash-ci / mix spark.formatter --check	5s
ash-ci / mix test	1m 4s
ash-ci / mix deps.unlock --check-unused	39s
ash-ci / Release	0s
	10m 11s

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