doc: clarify boolean parsing rules

Also fix a "MUST BE" typo

Co-Authored-By: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Morten Linderud <morten@linderud.pw>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
1 file changed