Add documentation for architectural decisions #847

Job	Run time
lint_compile	56s
test_diagnose	1m 26s
lint_dialyzer	3m 24s
lint_format	13s
lint_git	5s
lint_credo	55s
test_no_nif	45s
validate-changesets / Validate changesets	7s
test (1.18, 27)	56s
test (1.15, 26)	57s
test (1.19.5, 26)	59s
test (main, 28)	53s
test (latest, 28)	56s
test (1.16, 26)	1m 0s
test (1.12, 24)	1m 1s
test (1.17, 27)	53s
test (1.14, 25)	1m 2s
test (1.19.5, 27)	55s
test (1.13, 24)	1m 1s
test (1.19.5, 28)	1m 13s
test (1.11, 24)	1m 2s
	20m 39s

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