[ROM_EXT] Document Question About MTVEC
[ROM_EXT] Document Question About MTVEC

Signed-off-by: Sam Elliott <32a4841301e2f444934d6e427a2764482fa7a43d@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan