docs: add workflow guide, focused examples, and ExDoc integration #85

Job	Run time
Formatting	12s
Dialyzer	29s
Tests (ubuntu-latest / OTP 27.2 / Elixir 1.18.3)	28s
Credo	19s
Compile & Warnings	20s
Publish to Hex	1m 11s
	2m 59s

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