Add docs for derives #1919

Job	Run time
build (2_12, mima)	2m 1s
build (2_12, e2e)	5s
conformance	2m 42s
build (2_12, test)	14m 50s
build (2_13, mima)	2m 8s
build (2_13, e2e)	8s
build (2_13, test)	13m 9s
build (3, mima)	5s
build (3, e2e)	5s
build (3, test)	12m 55s
build (2_12, examples_and_formatting)	4m 6s
build (2_13, scala3_compat_test)	10m 32s
build (3, scala3_compat_test)	14m 5s
ci-passed	2s
	1h 16m 53s

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