The description for `key_value_separator` incorrectly states that this
separator is inserted between trailer lines, which appears likely to
have been incorrectly copied from `separator` when this option was
added.
Update the description to correctly indicate that it is a separator that
appears between the key and the value of each trailer.
Signed-off-by: Brian Lyles <redacted> Acked-by: Linus Arver <redacted> Signed-off-by: Junio C Hamano <redacted>