Add note about Result to `find_or_last` and `find_or_first` #995

Job	Run time
doc	8s
check	15s
check format	9s
check (--no-default-features)	15s
miri	2m 36s
msrv	49s
check (--no-default-features --features use_alloc)	26s
check (--all-targets --all-features)	30s
semver-checks	2m 38s
test	1m 4s
All checks succeeded	0s
	8m 50s

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