docs: Add cheatsheet documentation. #601

Job	Run time
ash-ci / audit	35s
ash-ci / MIX_ENV=test mix.compile	35s
ash-ci / mix igniter.upgrade	0s
ash-ci / Report Mix Dependencies	0s
ash-ci / mix spark.formatter --check	28s
ash-ci / mix format --check-formatted	21s
ash-ci / mix credo --strict	21s
ash-ci / MIX_ENV=dev mix.compile	20s
ash-ci / mix sobelow	20s
ash-ci / mix spark.cheat_sheets --check	41s
ash-ci / mix test	56s
ash-ci / mix deps.unlock --check-unused	23s
ash-ci / mix dialyzer	2m 37s
ash-ci / mix ash.codegen --check	0s
ash-ci / mix docs	1m 13s
ash-ci / Deploy docs to GitHub pages.	0s
ash-ci / NIF ${{ matrix.nif }} - ${{ matrix.job.target }} (${{ matrix.job.os }})	0s
ash-ci / Release	0s
	8m 50s

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