I've forgotten which version it is
Look at the file:
can I just add it to etc/fstab and reboot?
yes, as long as the partition you designate as SWAP is format as a swap.
(not sure if your just readding it, or changing swap partitions)
but if you want to get fancy, you don't have to reboot:
".. is format as a swap."
" is partitioned and formated as a swap."