fixup! PKCS7 and SMIME: improve documentation w.r.t. untrusted and si… #1479

Job	Run time
cygwin (windows-2019, win64, -DCMAKE_C_COMPILER=gcc --strict-warnings no-fips)	51m 19s
minimal (windows-2019)	12m 30s
minimal (windows-2022)	12m 34s
plain (windows-2019)	23m 22s
shared (windows-2019, win64, enable-fips)	37m 49s
plain (windows-2022)	24m 22s
shared (windows-2019, win32, --strict-warnings no-fips)	42m 46s
shared (windows-2022, win64, enable-fips)	47m 51s
shared (windows-2022, win32, --strict-warnings no-fips)	49m 36s
	5h 2m 9s

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