Add note about Result to `find_or_last` and `find_or_first` #1003

Job	Run time
check format	4s
miri	3m 3s
doc	7s
check	12s
check (--no-default-features)	8s
check (--no-default-features --features use_alloc)	9s
semver-checks	13s
check (--all-targets --all-features)	24s
msrv	58s
test	54s
All checks succeeded	0s
	6m 12s

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