docs: clarified that it is necessary to kill paths explicitely

Signed-off-by: Vitaly Chipounov <vitaly.chipounov@epfl.ch>
docs: reminder about concolic mode

Signed-off-by: Vitaly Chipounov <vitaly.chipounov@epfl.ch>
docs: fixed inconsistency

Signed-off-by: Vitaly Chipounov <vitaly.chipounov@epfl.ch>