add extra linting rules, update docs #348

Job	Run time
CI / Context	2s
CI / Generate matrix	12s
CI / Check governance	4s
CI / 8.1 mysql57 phplinting	2m 15s
CI / 8.2 sqlite3 phpunit all	10m 26s
CI / 8.1 prf-low sqlite3 phpunit all	14m 4s
CI / 8.1 sqlite3 phpunit all	9m 51s
CI / Dispatch tag patch release	3s
	36m 57s

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