Add note about creating unusable passwords #586

Job	Run time
Python 3.7, Database sqlite	1m 5s
Python 3.7, Database postgres	1m 17s
Python 3.8, Database sqlite	1m 35s
Python 3.8, Database postgres	1m 54s
Python 3.9, Database sqlite	1m 35s
Python 3.9, Database postgres	2m 4s
Python 3.10, Database sqlite	2m 6s
Python 3.10, Database postgres	2m 7s
Python 3.11, Database sqlite	1m 50s
Python 3.11, Database postgres	1m 32s
Python pypy-3.7, Database sqlite	1m 55s
Python pypy-3.7, Database postgres	1m 47s
Python pypy-3.8, Database sqlite	2m 36s
Python pypy-3.8, Database postgres	2m 37s
Python pypy-3.9, Database sqlite	2m 14s
Python pypy-3.9, Database postgres	2m 15s
	30m 29s

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